The difficulty of understanding these marvellous truths has
been glanced at by an old divine (see Things not generally
Known, p. 1); but the rarity of their full comprehension by
those unskilled in mathematical science is more powerfully
urged by Lord Brougham in these cogent terms:
Satisfying himself of the laws which regulate the mutual actions of
the planetary bodies, the mathematician can convince himself of a truth
yet more sublime than Newton’s discovery of gravitation, though flowing
from it; and must yield his assent to the marvellous position, that
all the irregularities occasioned in the system of the universe by the
mutual attraction of its members are periodical, and subject to an eternal
law, which prevents them from ever exceeding a stated amount, and
secures through all time the balanced structure of a universe composed
of bodies whose mighty bulk and prodigious swiftness of motion mock
the utmost efforts of the human imagination. All these truths are to
the skilful mathematician as thoroughly known, and their evidence is as
clear, as the simplest proposition of arithmetic to common understandings.
But how few are those who thus know and comprehend them!
Of all the millions that thoroughly believe these truths, certainly not a
thousand individuals are capable of following even any considerable portion
of the demonstrations upon which they rest; and probably not a
hundred now living have ever gone through the whole steps of these
demonstrations.—Dissertations on Subjects of Science connected with
Natural Theology, vol. ii.
Sir David Brewster thus impressively illustrates the same
subject:
Minds fitted and prepared for this species of inquiry are capable of
appreciating the great variety of evidence by which the truths of the
planetary system are established; but thousands of individuals, and
many who are highly distinguished in other branches of knowledge, are
incapable of understanding such researches, and view with a sceptical
eye the great and irrefragable truths of astronomy.
That the sun is stationary in the centre of our system; that the earth
moves round the sun, and round its own axis; that the diameter of
the earth is 8000 miles, and that of the sun one hundred and ten times
as great; that the earth’s orbit is 190,000,000 of miles in breadth; and
that if this immense space were filled with light, it would appear only
like a luminous point at the nearest fixed star,—are positions absolutely
unintelligible and incredible to all who have not carefully studied the
subject. To millions of our species, then, the great Book of Nature is
absolutely sealed; though it is in the power of all to unfold its pages, and
to peruse those glowing passages which proclaim the power and wisdom
of its Author.
Astronomy is a useful aid in discovering the Dates of ancient
Monuments. Thus, on the ceiling of a portico among the ruins
of Tentyris are the twelve signs of the Zodiac, placed according
to the apparent motion of the sun. According to this Zodiac,
the summer solstice is in Leo; from which it is easy to compute,
by the precession of the equinoxes of 50″·1 annually, that
the Zodiac of Tentyris must have been made 4000 years ago.
Mrs. Somerville relates that she once witnessed the ascertainment
of the date of a Papyrus by means of astronomy. The
manuscript was found in Egypt, in a mummy-case; and its antiquity
was determined by the configuration of the heavens at
the time of its construction. It proved to be a horoscope of the
time of Ptolemy.
This poetic designation dates back as far as the early period
of Anaximenes; but the first clearly defined signification of the
idea on which the term is based occurs in Empedocles. This
philosopher regarded the heaven of the fixed stars as a solid
mass, formed from the ether which had been rendered crystalline
by the action of fire.
In the Middle Ages, the fathers of the Church believed the
firmament to consist of from seven to ten glassy strata, incasing
each other like the different coatings of an onion. This
supposition still keeps its ground in some of the monasteries of
southern Europe, where Humboldt was greatly surprised to
hear a venerable prelate express an opinion in reference to the
fall of aerolites at Aigle, that the bodies we called meteoric
stones with vitrified crusts were not portions of the fallen stone
itself, but simply fragments of the crystal vault shattered by it
in its fall.
Empedocles maintained that the fixed stars were riveted to
the crystal heavens; but that the planets were free and unconstrained.
It is difficult to conceive how, according to Plato in
the Timæus, the fixed stars, riveted as they are to solid spheres,
could rotate independently.
Among the ancient views, it may be mentioned that the
equal distance at which the stars remained, while the whole vault
of heaven seemed to move from east to west, had led to the
idea of a firmament and a solid crystal sphere, in which Anaximenes
(who was probably not much later than Pythagoras)
had conjectured that the stars were riveted like nails.
The Pythagoreans, in applying their theory of numbers to
the geometrical consideration of the five regular bodies, to the
musical intervals of tone which determine a word and form
different kinds of sounds, extended it even to the system of
the universe itself; supposing that the moving, and, as it were,
vibrating planets, exciting sound-waves, must produce a spheral
music, according to the harmonic relations of their intervals of
space. “This music,” they add, “would be perceived by the
human ear, if it was not rendered insensible by extreme familiarity,
as it is perpetual, and men are accustomed to it from
childhood.”
The Pythagoreans affirm, in order to justify the reality of the tones
produced by the revolution of the spheres, that hearing takes place only
where there is an alternation of sound and silence. The inaudibility of
the spheral music is also accounted for by its overpowering the senses.
Aristotle himself calls the Pythagorean tone-myth pleasing and ingenious,
but untrue.
Plato attempted to illustrate the tones of the universe in an
agreeable picture, by attributing to each of the planetary spheres
a syren, who, supported by the stern daughters of Necessity,
the three Fates, maintain the eternal revolution of the world’s
axis. Mention is constantly made of the harmony of the
spheres, though generally reproachfully, throughout the writings
of Christian antiquity and the Middle Ages, from Basil the
Great to Thomas Aquinas and Petrus Alliacus.
At the close of the sixteenth century, Kepler revived these
musical ideas, and sought to trace out the analogies between
the relations of tone and the distances of the planets; and Tycho
Brahe was of opinion that the revolving conical bodies were
capable of vibrating the celestial air (what we now call “resisting
medium”) so as to produce tones. Yet Kepler, although he
had talked of Venus and the Earth sounding sharp in aphelion
and flat in perihelion, and the highest tone of Jupiter and that
of Venus coinciding in flat accord, positively declared there
to be “no such things as sounds among the heavenly bodies,
nor is their motion so turbulent as to elicit noise from the attrition
of the celestial air.” (See Things not generally Known, p. 44.)
Although this opinion was maintained incidentally by various
writers both on astronomy16 and natural religion, yet M.
Fontenelle was the first individual who wrote a treatise on the
Plurality of Worlds, which appeared in 1685, the year before the
publication of Newton’s Principia. Fontenelle’s work consists
of five chapters: 1. The earth is a planet which turns round
its axis, and also round the sun. 2. The moon is a habitable
world. 3. Particulars concerning the world in the moon, and
that the other planets are also inhabited. 4. Particulars of the
worlds of Venus, Mercury, Mars, Jupiter, and Saturn. 5. The
fixed stars are as many suns, each of which illuminates a world.
In a future edition, 1719, Fontenelle added, 6. New thoughts
which confirm those in the preceding conversations, and the
latest discoveries which have been made in the heavens. The
next work on the subject was the Theory of the Universe, or
Conjectures concerning the Celestial Bodies and their Inhabitants,
1698, by Christian Huygens, the contemporary of Newton.
The doctrine is maintained by almost all the distinguished
astronomers and writers who have flourished since the true
figure of the earth was determined. Giordano Bruna of Nola,
Kepler, and Tycho Brahe, believed in it; and Cardinal Cusa
and Bruno, before the discovery of binary systems among the
stars, believed also that the stars were inhabited. Sir Isaac
Newton likewise adopted the belief; and Dr. Bentley, Master
of Trinity College, Cambridge, in his eighth sermon on the Confutation
of Atheism from the origin and frame of the world,
has ably maintained the same doctrine. In our own day we
may number among its supporters the distinguished names of
the Marquis de la Place, Sir William and Sir John Herschel,
Dr. Chalmers, Isaac Taylor, and M. Arago. Dr. Chalmers maintains
the doctrine in his Astronomical Discourses, which one
Alexander Maxwell (who did not believe in the grand truths of
astronomy) attempted to controvert, in 1820, in a chapter of a
volume entitled Plurality of Worlds.
Next appeared Of a Plurality of Worlds, attributed to the
Rev. Dr. Whewell, Master of Trinity College, Cambridge; urging
the theological not less than the scientific reasons for believing
in the old tradition of a single world, and maintaining that “the
earth is really the largest planetary body in the solar system,—its
domestic hearth, and the only world in the universe.” “I
do not pretend,” says Dr. Whewell, “to disprove the plurality of
worlds; but I ask in vain for any argument which makes the
doctrine probable.” “It is too remote from knowledge to be
either proved or disproved.” Sir David Brewster has replied
to Dr. Whewell’s Essay, in More Worlds than One, the Creed
of the Philosopher and the Hope of the Christian, emphatically
maintaining that analogy strongly countenances the idea of all
the solar planets, if not all worlds in the universe, being peopled
with creatures not dissimilar in being and nature to the
inhabitants of the earth. This view is supported in Scientific
Certainties of Planetary Life, by T. C. Simon, who well treats one
point of the argument—that mere distance of the planets from
the central sun does not determine the condition as to light
and heat, but that the density of the ethereal medium enters
largely into the calculation. Mr. Simon’s general conclusion is,
that “neither on account of deficient or excessive heat, nor with
regard to the density of the materials, nor with regard to the force
of gravity on the surface, is there the slightest pretext for supposing
that all the planets of our system are not inhabited by
intellectual creatures with animal bodies like ourselves,—moral
beings, who know and love their great Maker, and who wait,
like the rest of His creation, upon His providence and upon His
care.” One of the leading points of Dr. Whewell’s Essay is, that
we should not elevate the conjectures of analogy into the rank
of scientific certainties; and that “the force of all the presumptions
drawn from physical reasoning for the opinion of planets
and stars being either inhabited or uninhabited is so small, that
the belief of all thoughtful persons on this subject will be determined
by moral, metaphysical, and theological considerations.”
Sir David Brewster, in his eloquent advocacy of the doctrine
of “more worlds than one,” thus argues for their peopling:
Man, in his future state of existence, is to consist, as at present,
of a spiritual nature residing in a corporeal frame. He must live, therefore,
upon a material planet, subject to all the laws of matter, and performing
functions for which a material body is indispensable. We must
consequently find for the race of Adam, if not races that may have
preceded him, a material home upon which they may reside, or by
which they may travel, by means unknown to us, to other localities in
the universe. At the present hour, the inhabitants of the earth are nearly
a thousand millions; and by whatever process we may compute the
numbers that have existed before the present generation, and estimate
those that are yet to inherit the earth, we shall obtain a population
which the habitable parts of our globe could not possibly accommodate.
If there is not room, then, on our earth for the millions of millions
of beings who have lived and died upon its surface, and who may yet
live and die during the period fixed for its occupation by man, we can
scarcely doubt that their future abode must be on some of the primary
or secondary planets of the solar system, whose inhabitants have ceased
to exist like those on the earth, or upon planets in our own or in other
systems which have been in a state of preparation, as our earth was,
for the advent of intellectual life.
Sir William Herschel, in 1785, conceived the happy idea
of counting the number of stars which passed at different
heights and in various directions over the field of view, of fifteen
minutes in diameter, of his twenty-feet reflecting telescope.
The field of view each time embraced only 1/833000th of
the whole heavens; and it would therefore require, according
to Struve, eighty-three years to gauge the whole sphere by a
similar process.
M. F. W. G. Struve gives as the splendid result of the
united studies of MM. Argelander, O. Struve, and Peters,
grounded on observations made at the three Russian observatories
of Dorpat, Abo, and Pulkowa, “that the velocity of the
motion of the solar system in space is such that the sun, with
all the bodies which depend upon it, advances annually towards
the constellation Hercules17 1·623 times the radius of the
earth’s orbit, or 33,550,000 geographical miles. The possible
error of this last number amounts to 1,733,000 geographical
miles, or to a seventh of the whole value. We may, then, wager
400,000 to 1 that the sun has a proper progressive motion, and
1 to 1 that it is comprised between the limits of thirty-eight
and twenty-nine millions of geographical miles.”
That is, taking 95,000,000 of English miles as the mean radius of
the Earth’s orbit, we have 95 × 1·623 = 154·185 millions of miles; and
consequently,
| |
English Miles. |
| The velocity of the Solar System |
154,185,000 |
in the year. |
| ”” |
422,424 |
in a day. |
| ”” |
17,601 |
in an hour. |
| ”” |
293 |
in a minute. |
| ”” |
57 |
in a second. |
The Sun and all his planets, primary and secondary, are therefore now
in rapid motion round an invisible focus. To that now dark and mysterious
centre, from which no ray, however feeble, shines, we may in
another age point our telescopes, detecting perchance the great luminary
which controls our system and bounds its path: into that vast
orbit man, during the whole cycle of his race, may never be allowed to
round.—North-British Review, No. 16.
M. Arago has found, by experiments with the polariscope,
that the light of gaseous bodies is natural light when it issues
from the burning surface; although this circumstance does not
prevent its subsequent complete polarisation, if subjected to
suitable reflections or refractions. Hence we obtain a most
simple method of discovering the nature of the sun at a distance
of forty millions of leagues. For if the light emanating from
the margin of the sun, and radiating from the solar substance
at an acute angle, reach us without having experienced any
sensible reflections or refractions in its passage to the earth,
and if it offer traces of polarisation, the sun must be a solid or
a liquid body. But if, on the contrary, the light emanating
from the sun’s margin give no indications of polarisation, the
incandescent portion of the sun must be gaseous. It is by means
of such a methodical sequence of observations that we may
acquire exact ideas regarding the physical constitution of the
sun.—Note to Humboldt’s Cosmos, vol. iii.
The extraordinary structure of the fully luminous Disc of
the Sun, as seen through Sir James South’s great achromatic,
in a drawing made by Mr. Gwilt, resembles compressed curd,
or white almond-soap, or a mass of asbestos fibres, lying in
a quaquaversus direction, and compressed into a solid mass.
There can be no illusion in this phenomenon; it is seen by
every person with good vision, and on every part of the sun’s
luminous surface or envelope, which is thus shown to be not
a flame, but a soft solid or thick fluid, maintained in an incandescent
state by subjacent heat, capable of being disturbed by
differences of temperature, and broken up as we see it when
the sun is covered with spots or openings in the luminous
matter.—North-British Review, No. 16.
Copernicus named the sun the lantern of the world (lucerna mundi);
and Theon of Smyrna called it the heart of the universe. The mass of
the sun is, according to Encke’s calculation of Sabine’s pendulum formula,
359,551 times that of the earth, or 355,499 times that of the earth
and moon together; whence the density of the sun is only about ¼ (or
more accurately 0·252) that of the earth. The volume of the sun is
600 times greater, and its mass, according to Galle, 738 times greater,
than that of all the planets combined. It may assist the mind in conceiving
a sensuous image of the magnitude of the sun, if we remember
that if the solar sphere were entirely hollowed out, and the earth placed
in its centre, there would still be room enough for the moon to describe
its orbit, even if the radius of the latter were increased 160,000 geographical
miles. A railway-engine, moving at the rate of thirty miles
an hour, would require 360 years to travel from the earth to the sun.
The diameter of the sun is rather more than one hundred and eleven
times the diameter of the earth. Therefore the volume or bulk of the
sun must be nearly one million four hundred thousand times that of the
earth. Lastly, if all the bodies composing the solar system were formed
into one globe, it would be only about the five-hundredth part of the
size of the sun.
The dilated size (generally) of the Sun or Moon, when seen
near the horizon, beyond what they appear to have when high
up in the sky, has nothing to do with refraction. It is an illusion
of the judgment, arising from the terrestrial objects interposed,
or placed in close comparison with them. In that situation
we view and judge of them as we do of terrestrial objects—in
detail, and with an acquired attention to parts. Aloft we
have no association to guide us, and their insulation in the
expanse of the sky leads us rather to undervalue than to over-rate
their apparent magnitudes. Actual measurement with a
proper instrument corrects our error, without, however, dispelling
our illusion. By this we learn that the sun, when just
on the horizon, subtends at our eyes almost exactly the same,
and the moon a materially less, angle than when seen at a
greater altitude in the sky, owing to its greater distance from
us in the former situation as compared with the latter.—Sir
John Herschel’s Outlines.
This phenomenon is the progressive motion of the centre
of gravity of the whole solar system in universal space. Its
velocity, according to Bessel, is probably four millions of miles
daily, in a relative velocity to that of 61 Cygni of at least
3,336,000 miles, or more than double the velocity of the revolution
of the earth in her orbit round the sun. This change of the
entire solar system would remain unknown to us, if the admirable
exactness of our astronomical instruments of measurement,
and the advancement recently made in the art of observing,
did not cause our progress towards remote stars to be
perceptible, like an approximation to the objects of a distant
shore in apparent motion. The proper motion of the star 61
Cygni, for instance, is so considerable, that it has amounted
to a whole degree in the course of 700 years.—Humboldt’s Cosmos,
vol. i.
Mr. Ponton has by means of a simple monochromatic photometer
ascertained that a small surface, illuminated by mean
solar light, is 444 times brighter than when it is illuminated by
a moderator lamp, and 1560 times brighter than when it is
illuminated by a wax-candle (short six in the lb.)—the artificial
light being in both instances placed at two inches’ distance
from the illuminated surface. And three electric lights, each
equal to 520 wax-candles, will render a small surface as bright
as when it is illuminated by mean sunshine.
It is thence inferred, that a stratum occupying the entire
surface of the sphere of which the earth’s distance from the
sun is the radius, and consisting of three layers of flame, each
1/1000th of an inch in thickness, each possessing a brightness
equal to that of such an electric light, and all three embraced
within a thickness of 1/40th of an inch, would give an amount
of illumination equal in quantity and intensity to that of the
sun at the distance of 95 millions of miles from his centre.
And were such a stratum transferred to the surface of the
sun, where it would occupy 46,275 times less area, its thickness
would be increased to 94 feet, and it would embrace
138,825 layers of flame, equal in brightness to the electric light;
but the same effect might be produced by a stratum about
nine miles in thickness, embracing 72 millions of layers, each
having only a brightness equal to that of a wax-candle.18
Mr. J. J. Waterston, in 1857, made at Bombay some experiments
on the photographic power of the sun’s direct light,
to obtain data in an inquiry as to the possibility of measuring
the diameter of the sun to a very minute fraction of a second,
by combining photography with the principle of the electric
telegraph; the first to measure the element space, the latter
the element time. The result is that about 1/20000th of a second
is sufficient exposure to the direct light of the sun to
obtain a distinct mark on a sensitive collodion plate, when
developed by the usual processes; and the duration of the
sun’s full action on any one point is about 1/9000th of a second.
M. Schatt, a young painter of Berlin, after 1500 experiments,
succeeded in establishing a scale of all the shades of
black which the action of the sun produces on photographic
paper; so that by comparing the shade obtained at any given
moment on a certain paper with that indicated on the scale,
the exact force of the sun’s light may be determined.
All moving power has its origin in the rays of the sun.
While Stephenson’s iron tubular railway-bridge over the Menai
Straits, 400 feet long, bends but half an inch under the heaviest
pressure of a train, it will bend up an inch and a half
from its usual horizontal line when the sun shines on it for
some hours. The Bunker-Hill monument, near Boston, U.S.,
is higher in the evening than in the morning of a sunny day;
the little sunbeams enter the pores of the stone like so many
wedges, lifting it up.
In winter, the Earth is nearer the Sun by about 1/30 than in
summer; but the rays strike the northern hemisphere more
obliquely in winter than the other half year.
M. Pouillet has estimated, with singular ingenuity, from a
series of observations made by himself, that the whole quantity
of heat which the Earth receives annually from the Sun is
such as would be sufficient to melt a stratum of ice covering
the entire globe forty-six feet deep.
By the action of the sun’s rays upon the earth, vegetables,
animals, and man, are in their turn supported; the rays become
likewise, as it were, a store of heat, and “the sources of
those great deposits of dynamical efficiency which are laid up
for human use in our coal strata” (Herschel).
A remarkable instance of the power of the sun’s rays is recorded
at Stonehouse Point, Devon, in the year 1828. To lay
the foundation of a sea-wall the workmen had to descend in a
diving-bell, which was fitted with convex glasses in the upper
part, by which, on several occasions in clear weather, the sun’s
rays were so concentrated as to burn the labourers’ clothes
when opposed to the focal point, and this when the bell was
twenty-five feet under the surface of the water!
Darkness of complexion has been attributed to the sun’s
power from the age of Solomon to this day,—“Look not upon
me, because I am black, because the sun hath looked upon
me:” and there cannot be a doubt that, to a certain degree,
the opinion is well founded. The invisible rays in the solar
beams, which change vegetable colour, and have been employed
with such remarkable effect in the daguerreotype, act
upon every substance on which they fall, producing mysterious
and wonderful changes in their molecular state, man not
excepted.—Mrs. Somerville.
The fluctuation in the sun’s direct heating power amounts
to 1/15th, which is too considerable a fraction of the whole intensity
not to aggravate in a serious degree the sufferings of
those who are exposed to it in thirsty deserts without shelter.
The amount of these sufferings, in the interior of Australia for
instance, are of the most frightful kind, and would seem far to
exceed what have ever been undergone by travellers in the
northern deserts of Africa. Thus Captain Sturt, in his account
of his Australian exploration, says: “The ground was almost
a molten surface; and if a match accidentally fell upon it, it
immediately ignited.” Sir John Herschel has observed the
temperature of the surface soil in South Africa as high as 159°
Fahrenheit. An ordinary lucifer-match does not ignite when
simply pressed upon a smooth surface at 212°; but in the act
of withdrawing it it takes fire, and the slightest friction upon
such a surface of course ignites it.
In order to compare the Light of the Sun with that of a
Star, Dr. Wollaston took as an intermediate object of comparison
the light of a candle reflected from a bulb about a quarter
of an inch in diameter, filled with quicksilver; and seen by one
eye through a lens of two inches focus, at the same time that
the star on the sun’s image, placed at a proper distance, was
viewed by the other eye through a telescope. The mean of
various trials seemed to show that the light of Sirius is equal
to that of the sun seen in a glass bulb 1/10th of an inch in diameter,
at the distance of 210 feet; or that they are in the
proportion of one to ten thousand millions: but as nearly one
half of this light is lost by reflection, the real proportion between
the light from Sirius and the sun is not greater than
that of one to twenty thousand millions.
Humboldt selects the following example from historical
records as to the occurrence of a sudden decrease in the light
of the Sun:
A.D. 33, the year of the Crucifixion. “Now from the sixth hour
there was darkness over all the land till the ninth hour” (St. Matthew
xxvii. 45). According to St. Luke (xxiii. 45), “the sun was darkened.”
In order to explain and corroborate these narrations, Eusebius brings
forward an eclipse of the sun in the 202d Olympiad, which had been
noticed by the chronicler Phlegon of Tralles (Ideler, Handbuch der
Mathem. Chronologie, Bd. ii. p. 417). Wurn, however, has shown that
the eclipse which occurred during this Olympiad, and was visible over
the whole of Asia Minor, must have happened as early as the 24th of
November 29 A.D. The day of the Crucifixion corresponded with the
Jewish Passover (Ideler, Bd. i. pp. 515–520), on the 14th of the month
Nisan, and the Passover was always celebrated at the time of the full
moon. The sun cannot therefore have been darkened for three hours by
the moon. The Jesuit Scheiner thinks the decrease in the light might
be ascribed to the occurrence of large sun-spots.
The important influence exerted by the Sun’s body, as a
mass, upon Terrestrial Magnetism, is confirmed by Sabine in
the ingenious observation, that the period at which the intensity
of the magnetic force is greatest, and the direction of the
needle most near to the vertical line, falls in both hemispheres
between the months of October and February; that is to say,
precisely at the time when the earth is nearest to the sun, and
moves in its orbit with the greatest velocity.
The Heat of the Sun is dissipated and lost by radiation, and
must be progressively diminished unless its thermal energy be
supplied. According to the measurements of M. Pouillet, the
quantity of heat given out by the sun in a year is equal to that
which would be produced by the combustion of a stratum of
coal seventeen miles in thickness; and if the sun’s capacity for
heat be assumed equal to that of water, and the heat be supposed
drawn uniformly from its entire mass, its temperature
would thereby undergo a diminution of 20·4° Fahr. annually.
On the other hand, there is a vast store of force in our system
capable of conversion into heat. If, as is indicated by the
small density of the sun, and by other circumstances, that
body has not yet reached the condition of incompressibility,
we have in the future approximation of its parts a fund of
heat, probably quite large enough to supply the wants of the
human family to the end of its sojourn here. It has been calculated
that an amount of condensation which would diminish
the diameter of the sun by only the ten-thousandth part, would
suffice to restore the heat emitted in 2000 years.
Mr. Sharp, of Dublin, exhibited to the British Association
in 1849 a Dial, consisting of a cylinder set to the day of the
month, and then elevated to the latitude. A thin plane of
metal, in the direction of its axis, is then turned by a milled
head below it till the shadow is a minimum, when a dial on
the top shows the hours by one hand, and the minutes by another,
to the precision of about three minutes.
During the summer, in the northern hemisphere, places
near the North Pole are in continual sunlight—the sun never
sets to them; while during that time places near the South
Pole never see the sun. When it is summer in the southern
hemisphere, and the sun shines on the South Pole without
setting, the North Pole is entirely deprived of his light. Indeed,
at the Poles there is but one day and one night; for the
sun shines for six months together on one Pole, and the other
six months on the other Pole.
Professor Airy, in his Six Lectures on Astronomy, gives a
masterly analysis of a problem of considerable intricacy, viz.
the determination of the parallax of the sun, and consequently
of his distance, by observations of the transit of Venus, the connecting
link between measures upon the earth’s surface and the
dimensions of our system. The further step of investigating
the parallax, and consequently the distance of the fixed stars
(where that is practicable), is also elucidated; and the author,
with evident satisfaction, thus sums up the several steps:
By means of a yard-measure, a base-line in a survey was measured;
from this, by the triangulations and computations of a survey, an arc of
meridian on the earth was measured; from this, with proper observations
with the zenith sector, the surveys being also repeated on different
parts of the earth, the earth’s form and dimensions were ascertained;
from these, and a previous independent knowledge of the proportions of
the distances of the earth and other planets from the sun, with observations
of the transit of Venus, the sun’s distance is determined; and from
this, with observations leading to the parallax of the stars, the distance
of the stars is determined. And every step in the process can be distinctly
referred to its basis, that is, the yard-measure.
Each of these bodies excites, by its attraction upon the
waters of the sea, two gigantic waves, which flow in the same
direction round the world as the attracting bodies themselves
apparently do. The two waves of the moon, on account of
her greater nearness, are about 3½ times as large as those excited
by the sun. One of these waves has its crest on the
quarter of the earth’s surface which is turned towards the
moon; the other is at the opposite side. Both these quarters
possess the flow of the tide, while the regions which lie between
have the ebb. Although in the open sea the height of
the tide amounts to only about three feet, and only in certain
narrow channels, where the moving water is squeezed together,
rises to thirty feet, the might of the phenomenon is nevertheless
manifest from the calculation of Bessel, according to
which a quarter of the earth covered by the sea possesses during
the flow of the tide about 25,000 cubic miles of water
more than during the ebb; and that, therefore, such a mass of
water must in 6¼ hours flow from one quarter of the earth to
the other.—Professor Helmholtz.
Sir John Herschel describes these phenomena, when watched
from day to day, or even from hour to hour, as appearing to enlarge
or contract, to change their forms, and at length disappear
altogether, or to break out anew in parts of the surface where
none were before. Occasionally they break up or divide into
two or more. The scale on which their movements takes place
is immense. A single second of angular measure, as seen from
the earth, corresponds on the sun’s disc to 461 miles; and a
circle of this diameter (containing therefore nearly 167,000
square miles) is the least space which can be distinctly discerned
on the sun as a visible area. Spots have been observed,
however, whose linear diameter has been upwards of 45,000
miles; and even, if some records are to be trusted, of very much
greater extent. That such a spot should close up in six weeks
time (for they seldom last much longer), its borders must approach
at the rate of more than 1000 miles a-day.
The same astronomer saw at the Cape of Good Hope, on the
29th March 1837, a solar spot occupying an area of near five
square minutes, equal to 3,780,000,000 square miles. “The
black centre of the spot of May 25th, 1837 (not the tenth part
of the preceding one), would have allowed the globe of our
earth to drop through it, leaving a thousand miles clear of
contact on all sides of that tremendous gulf.” For such an
amount of disturbance on the sun’s atmosphere, what reason
can be assigned?
The Rev. Mr. Dawes has invented a peculiar contrivance,
by means of which he has been enabled to scrutinise, under
high magnifying power, minute portions of the solar disc. He
places a metallic screen, pierced with a very small hole, in the
focus of the telescope, where the image of the sun is formed.
A small portion only of the image is thus allowed to pass
through, so that it may be examined by the eye-piece without
inconveniencing the observer by heat or glare. By this arrangement,
Mr. Dawes has observed peculiarities in the constitution
of the sun’s surface which are discernible in no other
way.
Before these observations, the dark spots seen on the sun’s
surface were supposed to be portions of the solid body of the
sun, laid bare to our view by those immense fluctuations in
the luminous regions of its atmosphere to which it appears to
be subject. It now appears that these dark portions are only
an additional and inferior stratum of a very feebly luminous
or illuminated portion of the sun’s atmosphere. This again in
its turn Mr. Dawes has frequently seen pierced with a smaller
and usually much more rounded aperture, which would seem
at last to afford a view of the real solar surface of most intense
blackness.
M. Schwabe, of Dessau, has discovered that the abundance
or paucity of spots displayed by the sun’s surface is subject to
a law of periodicity. This has been confirmed by M. Wolf, of
Berne, who shows that the period of these changes, from minimum
to minimum, is 11 years and 11-hundredths of a year,
being exactly at the rate of nine periods per century, the last
year of each century being a year of minimum. It is strongly
corroborative of the correctness both of M. Wolf’s period and
also of the periodicity itself, that of all the instances of the
appearance of spots on the sun recorded in history, even before
the invention of the telescope, or of remarkable deficiencies in
the sun’s light, of which there are great numbers, only two are
found to deviate as much as two years from M. Wolf’s epochs.
Sir William Herschel observed that the presence or absence of
spots had an influence on the temperature of the seasons; his
observations have been fully confirmed by M. Wolf. And, from
an examination of the chronicles of Zurich from A.D. 1000 to
A.D. 1800, he has come to the conclusion “that years rich in
solar spots are in general drier and more fruitful than those of
an opposite character; while the latter are wetter and more
stormy than the former.”
The most extraordinary fact, however, in connection with
the spots on the sun’s surface, is the singular coincidence of
their periods with those great disturbances in the magnetic
system of the earth to which the epithet of “magnetic storms”
has been affixed.
These disturbances, during which the magnetic needle is greatly
and universally agitated (not in a particular limited locality, but at one
and the same instant of time over whole continents, or even over the
whole earth), are found, so far as observation has hitherto extended,
to maintain a parallel, both in respect of their frequency of occurrence
and intensity in successive years, with the abundance and magnitude
of the spots in the same years, too close to be regarded as fortuitous.
The coincidence of the epochs of maxima and minima in the two series
of phenomena amounts, indeed, to identity; a fact evidently of most
important significance, but which neither astronomical nor magnetic
science is yet sufficiently advanced to interpret.—Herschel’s Outlines.
The signification and connection of the above varying phenomena
(Humboldt maintains) can never be manifested in their
entire importance until an uninterrupted series of representations
of the sun’s spots can be obtained by the aid of mechanical
clock-work and photographic apparatus, as the result
of prolonged observations during the many months of serene
weather enjoyed in a tropical climate.
M. Schwabe has thus distinguished himself as an indefatigable observer
of the sun’s spots, for his researches received the Royal Astronomical
Society’s Medal in 1857. “For thirty years,” said the President
at the presentation, “never has the sun exhibited his disc above the
horizon of Dessau without being confronted by Schwabe’s imperturbable
telescope; and that appears to have happened on an average about
300 days a-year. So, supposing that he had observed but once a-day,
he has made 9000 observations, in the course of which he discovered
about 4700 groups. This is, I believe, an instance of devoted persistence
unsurpassed in the annals of astronomy. The energy of one
man has revealed a phenomenon that had eluded the suspicion of astronomers
for 200 years.”
The Moon possesses neither Sea nor Atmosphere of appreciable
extent. Still, as a negative, in such case, is relative only
to the capabilities of the instruments employed, the search for
the indications of a lunar atmosphere has been renewed with
fresh augmentation of telescopic power. Of such indications,
the most delicate, perhaps, are those afforded by the occultation
of a planet by the moon. The occultation of Jupiter,
which took place on January 2, 1857, was observed with this
reference, and is said to have exhibited no hesitation, or change
of form or brightness, such as would be produced by the refraction
or absorption of an atmosphere. As respects the sea, if
water existed on the moon’s surface, the sun’s light reflected
from it should be completely polarised at a certain elongation
of the moon from the sun; and no traces of such light have
been observed.
MM. Baer and Maedler conclude that the moon is not entirely
without an atmosphere, but, owing to the smallness of
her mass, she is incapacitated from holding an extensive covering
of gas; and they add, “it is possible that this weak envelope
may sometimes, through local causes, in some measure
dim or condense itself.” But if any atmosphere exists on our
satellite, it must be, as Laplace says, more attenuated than
what is termed a vacuum in an air-pump.
Mr. Hopkins thinks that if there be any lunar atmosphere,
it must be very rare in comparison with the terrestrial atmosphere,
and inappreciable to the kind of observation by which
it has been tested; yet the absence of any refraction of the
light of the stars during occultation is a very refined test. Mr.
Nasmyth observes that “the sudden disappearance of the stars
behind the moon, without any change or diminution of her
brilliancy, is one of the most beautiful phenomena that can be
witnessed.”
Sir John Herschel observes: The fact of the moon turning
always the same face towards the earth is, in all probability,
the result of an elongation of its figure in the direction of a
line joining the centres of both the bodies, acting conjointly
with a non-coincidence of its centre of gravity with its centre
of symmetry.
If to this we add the supposition that the substance of the
moon is not homogeneous, and that some considerable preponderance
of weight is placed excentrically in it, it will be
easily apprehended that the portion of its surface nearer to that
heavier portion of its solid content, under all the circumstances
of the moon’s rotation, will permanently occupy the situation
most remote from the earth.
In what regards its assumption of a definite level, air obeys precisely
the same hydrostatical laws as water. The lunar atmosphere would
rest upon the lunar ocean, and form in its basin a lake of air, whose
upper portions at an altitude such as we are now contemplating would
be of excessive tenuity, especially should the provision of air be less
abundant in proportion than our own. It by no means follows, then,
from the absence of visible indications of water or air on this side of the
moon, that the other is equally destitute of them, and equally unfitted
for maintaining animal or vegetable life. Some slight approach to such
a state of things actually obtains on the earth itself. Nearly all the
land is collected in one of its hemispheres, and much the larger portion
of the sea in the opposite. There is evidently an excess of heavy material
vertically beneath the middle of the Pacific; while not very remote
from the point of the globe diametrically opposite rises the great table-land
of India and the Himalaya chain, on the summits of which the air
has not more than a third of the density it has on the sea-level, and
from which animated existence is for ever excluded.—Herschel’s Outlines,
5th edit.
The actual illumination of the lunar surface is not much
superior to that of weathered sandstone-rock in full sunshine.
Sir John Herschel has frequently compared the moon setting
behind the gray perpendicular façade of the Table Mountain
at the Cape of Good Hope, illuminated by the sun just risen
from the opposite quarter of the horizon, when it has been
scarcely distinguishable in brightness from the rock in contact
with it. The sun and moon being nearly at equal altitudes,
and the atmosphere perfectly free from cloud or vapour, its
effect is alike on both luminaries.
M. Zantedeschi has proved, by a long series of experiments
in the Botanic Gardens at Venice, Florence, and Padua, that,
contrary to the general opinion, the diffused rays of moonlight
have an influence upon the organs of plants, as the Sensitive
Plant and the Desmodium gyrans. The influence was feeble
compared with that of the sun; but the action is left beyond
further question.
Melloni has proved that the rays of the Moon give out a
slight degree of Heat (see Things not generally Known, p. 7);
and Professor Piazzi Smyth, from a point of the Peak of Teneriffe
8840 feet above the sea-level, has found distinctly perceptible
the heat radiated from the moon, which has been so
often sought for in vain in a lower region.
By means of the telescope, mountain-peaks are distinguished
in the ash-gray light of the larger spots and isolated brightly-shining
points of the moon, even when the disc is already
more than half illuminated. Lambert and Schroter have shown
that the extremely variable intensity of the ash-gray light of
the moon depends upon the greater or less degree of reflection
of the sunlight which falls upon the earth, according as it is
reflected from continuous continental masses, full of sandy deserts,
grassy steppes, tropical forests, and barren rocky ground,
or from large ocean surfaces. Lambert made the remarkable
observation (14th of February 1774) of a change of the ash-coloured
moonlight into an olive-green colour bordering upon
yellow. “The moon, which then stood vertically over the
Atlantic Ocean, received upon its right side the green terrestrial
light which is reflected towards her when the sky is clear
by the forest districts of South America.”
Plutarch says distinctly, in his remarkable work On the Face
in the Moon, that we may suppose the spots to be partly deep
chasms and valleys, partly mountain-peaks, which cast long
shadows, like Mount Athos, whose shadow reaches Lemnos.
The spots cover about two-fifths of the whole disc. In a clear
atmosphere, and under favourable circumstances in the position
of the moon, some of the spots are visible to the naked eye;
as the edge of the Apennines, the dark elevated plain Grimaldus,
the enclosed Mare Crisium, and Tycho, crowded round with
numerous mountain ridges and craters.
Professor Alexander remarks, that a map of the eastern
hemisphere, taken with the Bay of Bengal in the centre, would
bear a striking resemblance to the face of the moon presented
to us. The dark portions of the moon he considers to be continental
elevations, as shown by measuring the average height
of mountains above the dark and the light portions of the
moon.
The surface of the moon can be as distinctly seen by a good
telescope magnifying 1000 times, as it would be if not more
than 250 miles distant.
A circle of one second in diameter, as seen from the earth,
on the surface of the moon contains about a square mile.
Telescopes, therefore, must be greatly improved before we
could expect to see signs of inhabitants, as manifested by edifices
or changes on the surface of the soil. It should, however,
be observed, that owing to the small density of the materials of
the moon, and the comparatively feeble gravitation of bodies
on her surface, muscular force would there go six times as far
in overcoming the weight of materials as on the earth. Owing
to the want of air, however, it seems impossible that any form
of life analogous to those on earth can subsist there. No
appearance indicating vegetation, or the slightest variation of
surface which can in our opinion fairly be ascribed to change of
season, can any where be discerned.—Sir John Herschel’s Outlines.
In 1846, the Rev. Dr. Scoresby had the gratification of observing
the Moon through the stupendous telescope constructed
by Lord Rosse at Parsonstown. It appeared like a globe of
molten silver, and every object to the extent of 100 yards was
quite visible. Edifices, therefore, of the size of York Minster,
or even of the ruins of Whitby Abbey, might be easily perceived,
if they had existed. But there was no appearance of
any thing of that nature; neither was there any indication of
the existence of water, or of an atmosphere. There were a
great number of extinct volcanoes, several miles in breadth;
through one of them there was a line of continuance about 150
miles in length, which ran in a straight direction, like a railway.
The general appearance, however, was like one vast ruin
of nature; and many of the pieces of rock driven out of the
volcanoes appeared to lie at various distances.
By the aid of telescopes, we discern irregularities in the surface
of the moon which can be no other than mountains and
valleys,—for this plain reason, that we see the shadows cast
by the former in the exact proportion as to length which they
ought to have when we take into account the inclinations of
the sun’s rays to that part of the moon’s surface on which they
stand. From micrometrical measurements of the lengths of the
shadows of the more conspicuous mountains, Messrs. Baer and
Maedler have given a list of heights for no less than 1095 lunar
mountains, among which occur all degrees of elevation up to
22,823 British feet, or about 1400 feet higher than Chimborazo
in the Andes.
If Chimborazo were as high in proportion to the earth’s
diameter as a mountain in the moon known by the name of
Newton is to the moon’s diameter, its peak would be more
than sixteen miles high.
Arago calls to mind, that with a 6000-fold magnifying
power, which nevertheless could not be applied to the moon
with proportionate results, the mountains upon the moon
would appear to us just as Mont Blanc does to the naked eye
when seen from the Lake of Geneva.
We sometimes observe more than half the surface of the
moon, the eastern and northern edges being more visible at
one time, and the western or southern at another. By means
of this libration we are enabled to see the annular mountain
Malapert (which occasionally conceals the moon’s south pole),
the arctic landscape round the crater of Gioja, and the large
gray plane near Endymion, which conceals in superficial extent
the mare vaporum.
Three-sevenths of the moon are entirely concealed from our
observation; and must always remain so, unless some new and
unexpected disturbing causes come into play.—Humboldt.
The first object to which Galileo directed his telescope was the
mountainous parts of the moon, when he showed how their summits
might be measured: he found in the moon some circular districts surrounded
on all sides by mountains similar to the form of Bohemia.
The measurements of the mountains were made by the method of the
tangents of the solar ray. Galileo, as Helvetius did still later, measured
the distance of the summit of the mountains from the boundary of the
illuminated portion at the moment when the mountain summit was
first struck by the solar ray. Humboldt found no observations of the
lengths of the shadows of the mountains: the summits were “much
higher than the mountains on our earth.” The comparison is remarkable,
since, according to Riccioli, very exaggerated ideas of the height
of our mountains were then entertained. Galileo like all other observers
up to the close of the eighteenth century, believed in the existence of
many seas and of a lunar atmosphere.
The only influence of the Moon on the Weather of which
we have any decisive evidence is the tendency to disappearance
of clouds under the full moon, which Sir John Herschel refers
to its heat being much more readily absorbed in traversing
transparent media than direct solar heat, and being extinguished
in the upper regions of our atmosphere, never reaches the surface
of the atmosphere at all.
Mr. G. P. Bond of Cambridge, by some investigations to
ascertain whether the Attraction of the Moon has any effect
upon the motion of a pendulum, and consequently upon the
rate of a clock, has found the last to be changed to the amount
of 9/1000 of a second daily. At the equator the moon’s attraction
changes the weight of a body only 1/7000000 of the whole;
yet this force is sufficient to produce the vast phenomena of
the tides!
It is no slight evidence of the importance of analysis, that
Laplace’s perfect theory of tides has enabled us in our astronomical
ephemerides to predict the height of spring-tides at
the periods of new and full moon, and thus put the inhabitants
of the sea on their guard against the increased danger attending
the lunar revolutions.
As the form of the Earth exerts a powerful influence on the
motion of other cosmical bodies, and especially on that of its
neighbouring satellite, a more perfect knowledge of the motion
of the latter will enable us reciprocally to draw an inference
regarding the figure of the earth. Thus, as Laplace ably remarks:
“an astronomer, without leaving his observatory, may,
by a comparison of lunar theory with true observations, not
only be enabled to determine the form and size of the earth,
but also its distance from the sun and moon; results that otherwise
could only be arrived at by long and arduous expeditions
to the most remote parts of both hemispheres.” The compression
which may be inferred from lunar inequalities affords an
advantage not yielded by individual measurements of degrees
or experiments with the pendulum, since it gives a mean
amount which is referable to the whole planet.—Humboldt’s
Cosmos, vol. i.
The distance of the moon from the earth is about 240,000
miles; and if a railway-carriage were to travel at the rate of
1000 miles a-day, it would be eight months in reaching the
moon. But that is nothing compared with the length of time
it would occupy a locomotive to reach the sun from the earth:
if travelling at the rate of 1000 miles a-day, it would require
260 years to reach it.
As the Moon is at a very moderate distance from us (astronomically
speaking), and is in fact our nearest neighbour, while
the sun and stars are in comparison immensely beyond it, it
must of necessity happen that at one time or other it must
pass over, and occult or eclipse, every star or planet within its
zone, and, as seen from the surface of the earth, even somewhat
beyond it. Nor is the sun itself exempt from being thus
hidden whenever any part of the moon’s disc, in this her tortuous
course, comes to overlap any part of the space occupied
in the heavens by that luminary. On these occasions is exhibited
the most striking and impressive of all the occasional
phenomena of astronomy, an Eclipse of the Sun, in which a
greater or less portion, or even in some conjunctures the whole
of its disc, is obscured, and, as it were, obliterated, by the superposition
of that of the moon, which appears upon it as a
circularly-terminated black spot, producing a temporary diminution
of daylight, or even nocturnal darkness, so that the
stars appear as if at midnight.—Sir John Herschel’s Outlines.
The number of telescopic stars in the Milky Way uninterrupted
by any nebulæ is estimated at 18,000,000. To compare
this number with something analogous, Humboldt calls
attention to the fact, that there are not in the whole heavens
more than about 8000 stars, between the first and the sixth
magnitudes, visible to the naked eye. The barren astonishment
excited by numbers and dimensions in space when not
considered with reference to applications engaging the mental
and perceptive powers of man, is awakened in both extremes
of the universe—in the celestial bodies as in the minutest
animalcules. A cubic inch of the polishing slate of Bilin contains,
according to Ehrenberg, 40,000 millions of the siliceous
shells of Galionellæ.
Surely not (says Sir John Herschel) to illuminate our nights,
which an additional moon of the thousandth part of the size of
our own would do much better; nor to sparkle as a pageant
void of meaning and reality, and bewilder us among vain conjectures.
Useful, it is true, they are to man as points of exact
and permanent reference; but he must have studied astronomy
to little purpose, who can suppose man to be the only object of
his Creator’s care, or who does not see in the vast and wonderful
apparatus around us provision for other races of animated
beings. The planets derive their light from the sun; but that
cannot be the case with the stars. These doubtless, then, are
themselves suns; and may perhaps, each in its sphere, be the
presiding centre round which other planets, or bodies of which
we can form no conception from any analogy offered by our
own system, are circulating.19
Various estimates have been hazarded on the Number of
Stars throughout the whole heavens visible to us by the aid of
our colossal telescopes. Struve assumes for Herschel’s 20-feet
reflector, that a magnifying power of 180 would give 5,800,000
for the number of stars lying within the zones extending 30°
on either side of the equator, and 20,374,000 for the whole
heavens. Sir William Herschel conjectured that 18,000,000 of
stars in the Milky Way might be seen by his still more powerful
40-feet reflecting telescope.—Humboldt’s Cosmos, vol. iii.
The assumption that the extent of the starry firmament is
literally infinite has been made by Dr. Olbers the basis of a
conclusion that the celestial spaces are in some slight degree
deficient in transparency; so that all beyond a certain distance
is and must remain for ever unseen, the geometrical progression
of the extinction of light far outrunning the effect of any
conceivable increase in the power of our telescopes. Were it
not so, it is argued that every part of the celestial concave
ought to shine with the brightness of the solar disc, since no
visual ray could be so directed as not, in some point or other of
its infinite length, to encounter such a disc.—Edinburgh Review,
Jan. 1848.
Notwithstanding the great accuracy of the catalogued positions
of telescopic fixed stars and of modern star-maps, the
certainty of conviction that a star in the heavens has actually
disappeared since a certain epoch can only be arrived at
with great caution. Errors of actual observation, of reduction,
and of the press, often disfigure the very best catalogues. The
disappearance of a heavenly body from the place in which it
had been before distinctly seen, may be the result of its own
motion as much as of any such diminution of its photometric
process as would render the waves of light too weak to excite
our organs of sight. What we no longer see, is not necessarily
annihilated. The idea of destruction or combustion, as applied
to disappearing stars, belongs to the age of Tycho Brahe.
Even Pliny makes it a question. The apparent eternal cosmical
alternation of existence and destruction is not annihilation;
it is merely the transition of matter into new forms, into combinations
which are subject to new processes. Dark cosmical
bodies may by a renewed process of light again become luminous.—Humboldt’s
Cosmos, vol. iii.
Sir John Herschel, in his Outlines of Astronomy, thus shows
the changes in the celestial pole in 4000 years:
At the date of the erection of the Pyramid of Gizeh, which precedes
the present epoch by nearly 4000 years, the longitudes of all the stars
were less by 55° 45′ than at present. Calculating from this datum
the place of the pole of the heavens among the stars, it will be found
to fall near α Draconis; its distance from that star being 3° 44′ 25″.
This being the most conspicuous star in the immediate neighbourhood,
was therefore the Pole Star of that epoch. The latitude of Gizeh being
just 30° north, and consequently the altitude of the North Pole there
also 30°, it follows that the star in question must have had at its
lowest culmination at Gizeh an altitude of 25° 15′ 35″. Now it is a
remarkable fact, that of the nine pyramids still existing at Gizeh, six
(including all the largest) have the narrow passages by which alone they
can be entered (all which open out on the northern faces of their respective
pyramids) inclined to the horizon downwards at angles the
mean of which is 26° 47′. At the bottom of every one of these passages,
therefore, the Pole Star must have been visible at its lower culmination;
a circumstance which can hardly be supposed to have been unintentional,
and was doubtless connected (perhaps superstitiously) with the
astronomical observations of that star, of whose proximity to the pole
at the epoch of the erection of these wonderful structures we are thus
furnished with a monumental record of the most imperishable nature.
The Pleiades prove that, several thousand years ago even
as now, stars of the seventh magnitude were invisible to the
naked eye of average visual power. The group consists of
seven stars, of which six only, of the third, fourth, and fifth
magnitudes, could be readily distinguished. Of these Ovid
says (Fast. iv. 170):
“Quæ septem dici, sex tamen esse solent.”
Aratus states there were only six stars visible in the Pleiades.
One of the daughters of Atlas, Merope, the only one who
was wedded to a mortal, was said to have veiled herself for
very shame and to have disappeared. This is probably the
star of the seventh magnitude, which we call Celæne; for Hipparchus,
in his commentary on Aratus, observes that on clear
moonless nights seven stars may actually be seen.
The Pleiades were doubtless known to the rudest nations
from the earliest times; they are also called the mariner’s stars.
The name is from πλεῖν (plein), ‘to sail.’ The navigation of
the Mediterranean lasted from May to the beginning of November,
from the early rising to the early setting of the Pleiades.
In how many beautiful effusions of poetry and sentiment has
“the Lost Pleiad” been deplored!—and, to descend to more familiar
illustration of this group, the “Seven Stars,” the sailors’
favourites, and a frequent river-side public-house sign, may be
traced to the Pleiades.
The scintillation or twinkling of the stars is accompanied
by variations of colour, which have been remarked from a very
early age. M. Arago states, upon the authority of M. Babinet,
that the name of Barakesch, given by the Arabians to Sirius,
signifies the star of a thousand colours; and Tycho Brahe, Kepler,
and others, attest to similar change of colour in twinkling.
Even soon after the invention of the telescope, Simon Marius
remarked that by removing the eye-piece of the telescope the
images of the stars exhibited rapid fluctuations of brightness
and colour. In 1814 Nicholson applied to the telescope
a smart vibration, which caused the image of the star to be
transformed into a curved line of light returning into itself,
and diversified by several colours; each colour occupied about
a third of the whole length of the curve, and by applying ten
vibrations in a second, the light of Sirius in that time passed
through thirty changes of colour. Hence the stars in general
shine only by a portion of their light, the effect of twinkling
being to diminish their brightness. This phenomenon M. Arago
explains by the principle of the interference of light.
Ptolemy is said to have noted Sirius as a red star, though
it is now white. Sirius twinkles with red and blue light, and
Ptolemy’s eyes, like those of several other persons, may have
been more sensitive to the red than to the blue rays.—Sir David
Brewster’s More Worlds than One, p. 235.
Some of the double stars are of very different and dissimilar
colours; and to the revolving planetary bodies which apparently
circulate around them, a day lightened by a red light is succeeded
by, not a night, but a day equally brilliant, though illuminated
only by a green light.
Sir John Herschel wrote in 1833: “What is the distance
of the nearest fixed star? What is the scale on which our
visible firmament is constructed? And what proportion do its
dimensions bear to those of our own immediate system? To this,
however, astronomy has hitherto proved unable to supply an
answer. All we know on this subject is negative.” To these
questions, however, an answer can now be given. Slight
changes of position of some of the stars, called parallax, have
been distinctly observed and measured; and among these stars
No. 61 Cygni of Flamstead’s catalogue has a parallax of 5″, and
that of α Centauri has a proper motion of 4″ per annum.
The same astronomer states that each second of parallax indicates
a distance of 20 billions of miles, or 3¼ years’ journey of
light. Now the light sent to us by the sun, as compared with
that sent by Sirius and α Centauri, is about 22 thousand millions
to 1. “Hence, from the parallax assigned above to that
star, it is easy to conclude that its intrinsic splendour, as compared
with that of our sun at equal distances, is 2·3247, that
of the sun being unity. The light of Sirius is four times that
of α Centauri, and its parallax only 0·15″. This, in effect, ascribes
to it an intrinsic splendour equal to 96·63 times that of
α Centauri, and therefore 224·7 times that of our sun.”
This is justly regarded as one of the most brilliant triumphs
of astronomical science, for the delicacy of the investigation is
almost inconceivable; yet the reasoning is as unimpeachable
as the demonstration of a theorem of Euclid.
The bright star in the constellation of the Lyre, termed
Vega, is the brightest in the northern hemisphere; and the combined
researches of Struve, father and son, have found that
the distance of this star from the earth is no less than 130 billions
of miles! Light travelling at the rate of 192 thousand
miles in a second consequently occupies twenty-one years in
passing from this star to the earth. Now it has been found,
by comparing the light of Vega with the light of the sun, that
if the latter were removed to the distance of 130 billions of
miles, his apparent brightness would not amount to more than
the sixteenth part of the apparent brightness of Vega. We
are therefore warranted in concluding that the light of Vega
is equal to that of sixteen suns.
In illustration of the great diversity of the physical peculiarities
and probable condition of the planets, Sir John Herschel
describes the intensity of solar radiation as nearly seven times
greater on Mercury than on the earth, and on Uranus 330 times
less; the proportion between the two extremes being that of
upwards of 2000 to 1. Let any one figure to himself, (adds
Sir John,) the condition of our globe were the sun to be septupled,
to say nothing of the greater ratio; or were it diminished
to a seventh, or to a 300th of its actual power!
Again, the intensity of gravity, or its efficacy in counteracting
muscular power and repressing animal activity, on Jupiter
is nearly two-and-a-half times that on the earth; on
Mars not more than one-half; on the moon one-sixth; and on
the smaller planets probably not more than one-twentieth;
giving a scale of which the extremes are in the proportion of
sixty to one. Lastly, the density of Saturn hardly exceeds one-eighth
of the mean density of the earth, so that it must consist
of materials not much heavier than cork.
Jupiter is eleven times, Saturn ten times, Uranus five times, and
Neptune nearly six times, the diameter of our earth.
These four bodies revolve in space at such distances from the sun,
that if it were possible to start thence for each in succession, and to travel
at the railway speed of 33 miles per hour, the traveller would reach
| Jupiter in |
1712 |
years |
| Saturn |
3113 |
” |
| Uranus |
6226 |
” |
| Neptune |
9685 |
” |
If, therefore, a person had commenced his journey at the period of the
Christian era, he would now have to travel nearly 1300 years before he
would arrive at the planet Saturn; more than 4300 years before he
would reach Uranus; and no less than 7800 years before he could reach
the orbit of Neptune.
Yet the light which comes to us from these remote confines of the
solar system first issued from the sun, and is then reflected from the
surface of the planet. When the telescope is turned towards Neptune,
the observer’s eye sees the object by means of light that issued from
the sun eight hours before, and which since then has passed nearly
twice through that vast space which railway speed would require almost
a century of centuries to accomplish.—Bouvier’s Familiar Astronomy.
This discovery, one of the first fruits of the invention of the
telescope, and of Galileo’s early and happy idea of directing its
newly-found powers to the examination of the heavens, forms
one of the most memorable epochs in the history of astronomy.
The first astronomical solution of the great problem of the
longitude, practically the most important for the interests of
mankind which has ever been brought under the dominion of
strict scientific principles, dates immediately from this discovery.
The final and conclusive establishment of the Copernican
system of astronomy may also be considered as referable
to the discovery and study of this exquisite miniature system,
in which the laws of the planetary motions, as ascertained by
Kepler, and specially that which connects their periods and
distances, were specially traced, and found to be satisfactorily
maintained. And (as if to accumulate historical interest on
this point) it is to the observation of the eclipses of Jupiter’s
satellites that we owe the grand discovery of the aberration of
light, and the consequent determination of the enormous velocity
of that wonderful element—192,000 miles per second. Mr.
Dawes, in 1849, first noticed the existence of round, well-defined,
bright spots on the belts of Jupiter. They vary in situation
and number, as many as ten having been seen on one
occasion. As the belts of Jupiter have been ascribed to the
existence of currents analogous to our trade-winds, causing the
body of Jupiter to be visible through his cloudy atmosphere, Sir
John Herschel conjectures that those bright spots may possibly
be insulated masses of clouds of local origin, similar to the
cumuli which sometimes cap ascending columns of vapour in
our atmosphere.
It would require nearly 1300 globes of the size of our earth
to make one of the bulk of Jupiter. A railway-engine travelling
at the rate of thirty-three miles an hour would travel
round the earth in a month, but would require more than
eleven months to perform a journey round Jupiter.
In Maurice’s Indian Antiquities is an engraving of Sani,
the Saturn of the Hindoos, taken from an image in a very ancient
pagoda, which represents the deity encompassed by a ring
formed of two serpents. Hence it is inferred that the ancients
were acquainted with the existence of the ring of Saturn.
Arago mentions the remarkable fact of the ring and fourth
satellite of Saturn having been seen by Sir W. Herschel with
his smaller telescope by the naked eye, without any eye-piece.
The first or innermost of Saturn’s satellites is nearer to the
central body than any other of the secondary planets. Its distance
from the centre of Saturn is 80,088 miles; from the surface
of the planet 47,480 miles; and from the outmost edge of
the ring only 4916 miles. The traveller may form to himself
an estimate of the smallness of this amount by remembering
the statement of the well-known navigator, Captain Beechey,
that he had in three years passed over 72,800 miles.
According to very recent observations, Saturn’s ring is divided
into three separate rings, which, from the calculations
of Mr. Bond, an American astronomer, must be fluid. He is
of opinion that the number of rings is continually changing,
and that their maximum number, in the normal condition of
the mass, does not exceed twenty. Mr. Bond likewise maintains
that the power which sustains the centre of gravity of the ring
is not in the planet itself, but in its satellites; and the satellites,
though constantly disturbing the ring, actually sustain it in the
very act of perturbation. M. Otto Struve and Mr. Bond have
lately studied with the great Munich telescope, at the observatory
of Pulkowa, the third ring of Saturn, which Mr. Lassell and
Mr. Bond discovered to be fluid. They saw distinctly the dark
interval between this fluid ring and the two old ones, and even
measured its dimensions; and they perceived at its inner margin
an edge feebly illuminated, which they thought might be
the commencement of a fourth ring. These astronomers are of
opinion, that the fluid ring is not of very recent formation, and
that it is not subject to rapid change; and they have come to
the extraordinary conclusion, that the inner border of the ring
has, since the time of Huygens, been gradually approaching to
the body of Saturn, and that we may expect, sooner or later,
perhaps in some dozen of years, to see the rings united with the
body of the planet. But this theory is by other observers pronounced
untenable.
Mercury being so much nearer to the Sun than the Earth,
he receives, it is supposed, seven times more heat than the
earth. Mrs. Somerville says: “On Mercury, the mean heat
arising from the intensity of the sun’s rays must be above that
of boiling quicksilver, and water would boil even at the poles.”
But he may be provided with an atmosphere so constituted as
to absorb or reflect a great portion of the superabundant heat;
so that his inhabitants (if he have any) may enjoy a climate as
temperate as any on our globe.
The most remarkable peculiarities of these ultra-zodiacal
planets, according to Sir John Herschel, must lie in this condition
of their state: a man placed on one of them would spring
with ease sixty feet high, and sustain no greater shock in his
descent than he does on the earth from leaping a yard. On
such planets, giants might exist; and those enormous animals
which on the earth require the buoyant power of water to counteract
their weight, might there be denizens of the land. But
of such speculations there is no end.
The opponents of the doctrine of the Plurality of Worlds
allow that a greater probability exists of Mars being inhabited
than in the case of any other planet. His diameter is 4100
miles; and his surface exhibits spots of different hues,—the
seas, according to Sir John Herschel, being green, and the land
red. “The variety in the spots,” says this astronomer, “may
arise from the planet not being destitute of atmosphere and
cloud; and what adds greatly to the probability of this, is the
appearance of brilliant white spots at its poles, which have
been conjectured, with some probability, to be snow, as they
disappear when they have been long exposed to the sun, and are
greatest when emerging from the long night of their polar
winter, the snow-line then extending to about six degrees from
the pole.” “The length of the day,” says Sir David Brewster,
“is almost exactly twenty-four hours,—the same as that
of the earth. Continents and oceans and green savannahs
have been observed upon Mars, and the snow of his polar regions
has been seen to disappear with the heat of summer.”
We actually see the clouds floating in the atmosphere of Mars,
and there is the appearance of land and water on his disc.
In a sketch of this planet, as seen in the pure atmosphere of
Calcutta by Mr. Grant, it appears, to use his words, “actually
as a little world,” and as the earth would appear at a distance,
with its seas and continents of different shades. As the diameter
of Mars is only about one half that of our earth, the
weight of bodies will be about one half what it would be if they
were placed upon our globe.
This noble discovery marked in a signal manner the maturity
of astronomical science. The proof, or at least the urgent
presumption, of the existence of such a planet, as a means
of accounting (by its attraction) for certain small irregularities
observed in the motions of Uranus, was afforded almost simultaneously
by the independent researches of two geometers,
Mr. Adams of Cambridge, and M. Leverrier of Paris, who were
enabled from theory alone to calculate whereabouts it ought
to appear in the heavens, if visible, the places thus independently
calculated agreeing surprisingly. Within a single degree
of the place assigned by M. Leverrier’s calculations, and
by him communicated to Dr. Galle of the Royal Observatory
at Berlin, it was actually found by that astronomer on the very
first night after the receipt of that communication, on turning
a telescope on the spot, and comparing the stars in its immediate
neighbourhood with those previously laid down in one of
the zodiacal charts. This remarkable verification of an indication
so extraordinary took place on the 23d of September 1846.20—Sir
John Herschel’s Outlines.
Neptune revolves round the sun in about 172 years, at a
mean distance of thirty,—that of Uranus being nineteen, and
that of the earth one: and by its discovery the solar system
has been extended one thousand millions of miles beyond its
former limit.
Neptune is suspected to have a ring, but the suspicion has
not been confirmed. It has been demonstrated by the observations
of Mr. Lassell, M. Otto Struve, and Mr. Bond, to be
attended by at least one satellite.
One of the most curious facts brought to light by the discovery
of Neptune, is the failure of Bode’s law to give an approximation
to its distance from the sun; a striking exemplification
of the danger of trusting to the universal applicability
of an empirical law. After standing the severe test which led
to the discovery of the asteroids, it seemed almost contrary to
the laws of probability that the discovery of another member
of the planetary system should prove its failure as an universal
rule.
Although Comets have a smaller mass than any other cosmical
bodies—being, according to our present knowledge, probably
not equal to 1/5000th part of the earth’s mass—yet they
occupy the largest space, as their tails in several instances extend
over many millions of miles. The cone of luminous vapour
which radiates from them has been found in some cases
(as in 1680 and 1811) equal to the length of the earth’s distance
from the sun, forming a line that intersects both the orbits of
Venus and Mercury. It is even probable that the vapour of
the tails of comets mingled with our atmosphere in the years
1819 and 1823.—Humboldt’s Cosmos, vol. i.
The phenomenon of the tail of a Comet being visible in
bright Sunshine, which is recorded of the comet of 1402, occurred
again in the case of the large comet of 1843, whose
nucleus and tail were seen in North America on February 28th
(according to the testimony of J. G. Clarke, of Portland, State
of Maine), between one and three o’clock in the afternoon.
The distance of the very dense nucleus from the sun’s light
admitted of being measured with much exactness. The nucleus
and tail (a darker space intervening) appeared like a very
pure white cloud.—American Journal of Science, vol. xiv.
E. C. Otté, the translator of Bohn’s edition of Humboldt’s
Cosmos, at New Bedford, Massachusetts, U.S., Feb. 28th, 1843,
distinctly saw the above comet between one and two in the
afternoon. The sky at the time was intensely blue, and the
sun shining with a dazzling brightness unknown in European
climates.
This very remarkable Comet, seen in England on the 17th
of March 1843, had a nucleus with the appearance of a planetary
disc, and the brightness of a star of the first or second magnitude.
It had a double tail divided by a dark line. At the
Cape of Good Hope it was seen in full daylight, and in the immediate
vicinity of the sea; but the most remarkable fact in
its history was its near approach to the sun, its distance from
his surface being only one-fourteenth of his diameter. The heat
to which it was exposed, therefore, was much greater than that
which Sir Isaac Newton ascribed to the comet of 1680, namely
200 times that of red-hot iron. Sir John Herschel has computed
that it must have been 24 times greater than that which
was produced in the focus of Parker’s burning lens, 32 inches
in diameter, which melts crystals of quartz and agate.21
M. Struve of Pulkowa has compared Sir William Herschel’s
opinion on this subject, as maintained in 1785, with that to
which he was subsequently led; and arrives at the conclusion
that, according to Sir W. Herschel himself, the visible extent
of the Milky Way increases with the penetrating power of the
telescopes employed; that it is impossible to discover by his
instruments the termination of the Milky Way (as an independent
cluster of stars); and that even his gigantic telescope
of forty feet focal length does not enable him to extend our
knowledge of the Milky Way, which is incapable of being
sounded. Sir William Herschel’s Theory of the Milky Way was
as follows: He considered our solar system, and all the stars
which we can see with the eye, as placed within, and constituting
a part of, the nebula of the Milky Way, a congeries of
many millions of stars, so that the projection of these stars
must form a luminous track on the concavity of the sky; and
by estimating or counting the number of stars in different directions,
he was able to form a rude judgment of the probable
form of the nebula, and of the probable position of the solar
system within it.
This remarkable belt has maintained from the earliest ages
the same relative situation among the stars; and, when examined
through powerful telescopes, is found (wonderful to
relate!) to consist entirely of stars scattered by millions, like
glittering dust, on the black ground of the general heavens.
These are truly astounding. Sir William Herschel estimated
the distance of the annular nebula between Beta and
Gamma Lyræ to be from our system 950 times that of Sirius;
and a globular cluster about 5½° south-east of Beta Sir William
computed to be one thousand three hundred billions of miles
from our system. Again, in Scutum Sobieski is one nebula in
the shape of a horseshoe; but which, when viewed with high
magnifying power, presents a different appearance. Sir William
Herschel estimated this nebula to be 900 times farther from us
than Sirius. In some parts of its vicinity he observed 588
stars in his telescope at one time; and he counted 258,000 in
a space 10° long and 2½° wide. There is a globular cluster
between the mouths of Pegasus and Equuleus, which Sir William
Herschel estimated to be 243 times farther from us than
Sirius. Caroline Herschel discovered in the right foot of Andromeda
a nebula of enormous dimensions, placed at an inconceivable
distance from us: it consists probably of myriads of
solar systems, which, taken together, are but a point in the
universe. The nebula about 10° west of the principal star in
Triangulum is supposed by Sir William Herschel to be 344
times the distance of Sirius from the earth, which would be the
immense sum of nearly seventeen thousand billions of miles
from our planet.
After the straining mind has exhausted all its resources in
attempting to fathom the distance of the smallest telescopic
star, or the faintest nebula, it has reached only the visible confines
of the sidereal creation. The universe of stars is but an
atom in the universe of space; above it, and beneath it, and
around it, there is still infinity.
The commencement of our Planetary System, including the
sun, must, according to Kant and Laplace, be regarded as an
immense nebulous mass filling the portion of space which is
now occupied by our system far beyond the limits of Neptune,
our most distant planet. Even now we perhaps see similar
masses in the distant regions of the firmament, as patches of
nebulæ, and nebulous stars; within our system also, comets,
the zodiacal light, the corona of the sun during a total eclipse,
exhibit resemblances of a nebulous substance, which is so thin
that the light of the stars passes through it unenfeebled and
unrefracted. If we calculate the density of the mass of our
planetary system, according to the above assumption, for the
time when it was a nebulous sphere which reached to the path
of the outmost planet, we should find that it would require
several cubic miles of such matter to weigh a single grain.—Professor
Helmholtz.
A quarter of a century ago, Sir John Herschel expressed his
opinion that those nebulæ which were not resolved into individual
stars by the highest powers then used, might be hereafter
completely resolved by a further increase of optical power:
In fact, this probability has almost been converted into a certainty
by the magnificent reflecting telescope constructed by Lord Rosse, of
6 feet in aperture, which has resolved, or rendered resolvable, multitudes
of nebulæ which had resisted all inferior powers. The sublimity of the
spectacle afforded by that instrument of some of the larger globular and
other clusters is declared by all who have witnessed it to be such as no
words can express.23
Although, therefore, nebulæ do exist, which even in this powerful
telescope appear as nebulæ, without any sign of resolution, it may very
reasonably be doubted whether there be really any essential physical
distinction between nebulæ and clusters of stars, at least in the nature of
the matter of which they consist; and whether the distinction between
such nebulæ as are easily resolved, barely resolvable with excellent telescopes,
and altogether irresolvable with the best, be any thing else than
one of degree, arising merely from the excessive minuteness and multitude
of the stars of which the latter, as compared with the former, consist.—Outlines
of Astronomy, 5th edit. 1858.
It should be added, that Sir John Herschel considers the
“nebular hypothesis” and the above theory of sidereal aggregation
to stand quite independent of each other.
Professor Helmholtz, assuming that at the commencement
the density of the nebulous matter was a vanishing quantity,
as compared with the present density of the sun and planets,
calculates how much work has been performed by the condensation;
how much of this work still exists in the form of mechanical
force, as attraction of the planets towards the sun, and
as vis viva of their motion; and finds by this how much of the
force has been converted into heat.
The result of this calculation is, that only about the 45th part of
the original mechanical force remains as such, and that the remainder,
converted into heat, would be sufficient to raise a mass of water equal to
the sun and planets taken together, not less than 28,000,000 of degrees
of the centigrade scale. For the sake of comparison, Professor Helmholtz
mentions that the highest temperature which we can produce by
the oxy-hydrogen blowpipe, which is sufficient to vaporise even platina,
and which but few bodies can endure, is estimated at about 2000 degrees.
Of the action of a temperature of 28,000,000 of such degrees we can
form no notion. If the mass of our entire system were of pure coal,
by the combustion of the whole of it only the 350th part of the above
quantity would be generated.
The store of force at present possessed by our system is equivalent
to immense quantities of heat. If our earth were by a sudden shock
brought to rest in her orbit—which is not to be feared in the existing
arrangement of our system—by such a shock a quantity of heat would
be generated equal to that produced by the combustion of fourteen such
earths of solid coal. Making the most unfavourable assumption as to
its capacity for heat, that is, placing it equal to that of water, the mass
of the earth would thereby be heated 11,200°; it would therefore be quite
fused, and for the most part reduced to vapour. If, then, the earth,
after having been thus brought to rest, should fall into the sun, which
of course would be the case, the quantity of heat developed by the shock
would be 400 times greater.
The most fertile region in astronomical discovery during
the last quarter of a century has been the planetary members
of the solar system. In 1833, Sir John Herschel enumerated ten
planets as visible from the earth, either by the unaided eye or
by the telescope; the number is now increased more than fivefold.
With the exception of Neptune, the discovery of new
planets is confined to the class called Asteroids. These all
revolve in elliptic orbits between those of Jupiter and Mars.
Zitius of Wittemberg discovered an empirical law, which
seemed to govern the distances of the planets from the sun;
but there was a remarkable interruption in the law, according
to which a planet ought to have been placed between Mars and
Jupiter. Professor Bode of Berlin directed the attention of
astronomers to the possibility of such a planet existing; and
in seven years’ observations from the commencement of the
present century, not one but four planets were found, differing
widely from one another in the elements of their orbits, but
agreeing very nearly at their mean distances from the sun with
that of the supposed planet. This curious coincidence of the
mean distances of these four asteroids with the planet according
to Bode’s law, as it is generally called, led to the conjecture
that these four planets were but fragments of the missing
planet, blown to atoms by some internal explosion, and that
many more fragments might exist, and be possibly discovered
by diligent search.
Concerning this apparently wild hypothesis, Sir John Herschel
offered the following remarkable apology: “This may
serve as a specimen of the dreams in which astronomers, like
other speculators, occasionally and harmlessly indulge.”
The dream, wild as it appeared, has been realised now. Sir
John, in the fifth edition of his Outlines of Astronomy, published
in 1858, tells us:
Whatever may be thought of such a speculation as a physical hypothesis,
this conclusion has been verified to a considerable extent as a
matter of fact by subsequent discovery, the result of a careful and minute
examination and mapping down of the smaller stars in and near
the zodiac, undertaken with that express object. Zodiacal charts of this
kind, the product of the zeal and industry of many astronomers, have
been constructed, in which every star down to the ninth, tenth, or even
lower magnitudes, is inserted; and these stars being compared with the
actual stars of the heavens, the intrusion of any stranger within their
limits cannot fail to be noticed when the comparison is systematically
conducted. The discovery of Astræa and Hebe by Professor Hencke,
in 1845 and 1847, revived the flagging spirit of inquiry in this direction;
with what success, the list of fifty-two asteroids, with their names and
the dates of their discovery, will best show. The labours of our indefatigable
countryman, Mr. Hind, have been rewarded by the discovery of
no less than eight of them.
Humboldt relates, that a friend at Popayan, at an elevation
of 5583 feet above the sea-level, at noon, when the sun was
shining brightly in a cloudless sky, saw his room lighted up by
a fire-ball: he had his back towards the window at the time,
and on turning round, perceived that great part of the path
traversed by the fire-ball was still illuminated by the brightest
radiance. The Germans call these phenomena star-snuff, from
the vulgar notion that the lights in the firmament undergo a
process of snuffing, or cleaning. Other nations call it a shot or
fall of stars, and the English star-shoot. Certain tribes of the
Orinoco term the pearly drops of dew which cover the beautiful
leaves of the heliconia star-spit. In the Lithuanian mythology,
the nature and signification of falling stars are embodied under
nobler and more graceful symbols. The Parcæ, Werpeja, weave
in heaven for the new-born child its thread of fate, attaching
each separate thread to a star. When death approaches the
person, the thread is rent, and the star wanes and sinks to the
earth.—Jacob Grimm.
In the perpetual vicissitude of theoretical views, says the
author of Giordano Bruno, “most men see nothing in philosophy
but a succession of passing meteors; whilst even the
grander forms in which she has revealed herself share the fate
of comets,—bodies that do not rank in popular opinion amongst
the external and permanent works of nature, but are regarded
as mere fugitive apparitions of igneous vapour.”
The hypothesis of the selenic origin of meteoric stones depends
upon a number of conditions, the accidental coincidence
of which could alone convert a possible to an actual fact. The
view of the original existence of small planetary masses in space
is simpler, and at the same time more analogous with those
entertained concerning the formation of other portions of the
solar system.
Diogenes Laertius thought aerolites came from the sun; but Pliny
derides this theory. The fall of aerolites in bright sunshine, and when
the moon’s disc was invisible, probably led to the idea of sun-stones.
Moreover Anaxagoras regarded the sun as “a molten fiery mass;” and
Euripides, in Phaëton, terms the sun “a golden mass,” that is to say,
a fire-coloured, brightly-shining matter, but not leading to the inference
that aerolites are golden sun-stones. The Greek philosophers had
four hypotheses as to their origin: telluric, from ascending exhalations;
masses of stone raised by hurricanes; a solar origin; and lastly, an
origin in the regions of space, as heavenly bodies which had long remained
invisible: the last opinion entirely according with that of the
present day.
Chladni states that an Italian physicist, Paolo Maria Terzago, on
the occasion of the fall of an aerolite at Milan, in 1660, by which a Franciscan
monk was killed, was the first who surmised that aerolites were
of selenic origin. Without any previous knowledge of this conjecture,
Olbers was led, in 1795 (after the celebrated fall at Siena, June 16th,
1794), to investigate the amount of the initial tangential force that
would be required to bring to the earth masses projected from the
moon. Olbers, Brandes, and Chaldni thought that “the velocity of 16
to 32 miles, with which fire-balls and shooting-stars entered our atmosphere,”
furnished a refutation to the view of their selenic origin. According
to Olbers, it would require to reach the earth, setting aside the
resistance of the air, an initial velocity of 8292 feet in the second; according
to Laplace, 7862; to Biot, 8282; and to Poisson, 7595. Laplace
states that this velocity is only five or six times as great as that of a
cannon-ball; but Olbers has shown that “with such an initial velocity
as 7500 or 8000 feet in a second, meteoric stones would arrive at the
surface of our earth with a velocity of only 35,000 feet.” But the measured
velocity of meteoric stones averages upwards of 114,000 feet to a
second; consequently the original velocity of projection from the moon
must be almost 110,000 feet, and therefore 14 times greater than Laplace
asserted. It must, however, be recollected, that the opinion then so prevalent,
of the existence of active volcanoes in the moon, where air and
water are absent, has since been abandoned.
Laplace elsewhere states, that in all probability aerolites “come
from the depths of space;” yet he in another passage inclines to the hypothesis
of their lunar origin, always, however, assuming that the stones
projected from the moon “become satellites of our earth, describing
around it more or less eccentric orbits, and thus not reaching its atmosphere
until several or even many revolutions have been accomplished.”
In Syria there is a popular belief that aerolites chiefly fall on clear
moonlight nights. The ancients (Pliny tells us) looked for their fall
during lunar eclipses.—Abridged from Humboldt’s Cosmos, vol. i. (Bohn’s
edition).
Dr. Laurence Smith, U.S., accepts the “lunar theory,” and
considers meteorites to be masses thrown off from the moon,
the attractive power of which is but one-sixth that of the earth;
so that bodies thrown from the surface of the moon experience
but one sixth the retarding force they would have when thrown
from the earth’s surface.
Look again (says Dr. Smith) at the constitution of the meteorite,
made up principally of pure iron. It came evidently from some place
where there is little or no oxygen. Now the moon has no atmosphere,
and no water on its surface. There is no oxygen there. Hurled from
the moon, these bodies,—these masses of almost pure iron,—would
flame in the sun like polished steel, and on reaching our atmosphere
would burn in its oxygen until a black oxide cooled it; and this we find
to be the case with all meteorites,—the black colour is only an external
covering.
Sir Humphry Davy, from facts contained in his researches
on flame, in 1817, conceives that the light of meteors depends,
not upon the ignition of inflammable gases, but upon that of
solid bodies; that such is their velocity of motion, as to excite
sufficient heat for their ignition by the compression even of
rare air; and that the phenomena of falling stars may be explained
by regarding them as small incombustible bodies moving
round the earth in very eccentric orbits, and becoming
ignited only when they pass with immense rapidity through
the upper regions of the atmosphere; whilst those meteors
which throw down stony bodies are, similarly circumstanced,
combustible masses.
Masses of iron and nickel, having all the appearance of
aerolites or meteoric stones, have been discovered in Siberia,
at a depth of ten metres below the surface of the earth. From
the fact, however, that no meteoric stones are found in the
secondary and tertiary formations, it would seem to follow that
the phenomena of falling stones did not take place till the earth
assumed its present conditions.
The most magnificent Shower of Meteors that has ever been
known was that which fell during the night of November 12th,
1833, commencing at nine o’clock in the evening, and continuing
till the morning sun concealed the meteors from view. This
shower extended from Canada to the northern boundary of South
America, and over a tract of nearly 3000 miles in width.
Mrs. Somerville mentions a Meteorite which passed within
twenty-five miles of our planet, and was estimated to weigh
600,000 tons, and to move with a velocity of twenty miles in a
second. Only a small fragment of this immense mass reached
the earth. Four instances are recorded of persons being killed
by their fall. A block of stone fell at Ægos Potamos, B.C. 465,
as large as two millstones; another at Narni, in 921, projected
like a rock four feet above the surface of the river, in which it
was seen to fall. The Emperor Jehangire had a sword forged
from a mass of meteoric iron, which fell in 1620 at Jahlinder
in the Punjab. Sixteen instances of the fall of stones in the
British Isles are well authenticated to have occurred since 1620,
one of them in London. It is very remarkable that no new
chemical element has been detected in any of the numerous
meteorites which have been analysed.
It is (says Olbers) a remarkable but hitherto unregarded
fact, that while shells are found in secondary and tertiary formations,
no Fossil Meteoric Stones have as yet been discovered.
May we conclude from this circumstance, that previous to the
present and last modification of the earth’s surface no meteoric
stones fell on it, though at the present time it appears probable,
from the researches of Schreibers, that 700 fall annually?24
While all the phenomena in the heavens indicate a law of
progressive creation, in which revolving matter is distributed
into suns and planets, there are indications in our own system
that a period has been assigned for its duration, which, sooner
or later, it must reach. The medium which fills universal
space, whether it be a luminiferous ether, or arise from the
indefinite expansion of planetary atmospheres, must retard the
bodies which move in it, even were it 360,000 millions of times
more rare than atmospheric air; and, with its time of revolution
gradually shortening, the satellite must return to its
planet, the planet to its sun, and the sun to its primeval nebula.
The fate of our system, thus deduced from mechanical laws,
must be the fate of all others. Motion cannot be perpetuated
in a resisting medium; and where there exist disturbing forces,
there must be primarily derangement, and ultimately ruin.
From the great central mass, heat may again be summoned to
exhale nebulous matter; chemical forces may again produce
motion, and motion may again generate systems; but, as in
the recurring catastrophes which have desolated our earth, the
great First Cause must preside at the dawn of each cosmical
cycle; and, as in the animal races which were successively reproduced,
new celestial creations of a nobler form of beauty
and of a higher form of permanence may yet appear in the
sidereal universe. “Behold, I create new heavens and a new
earth, and the former shall not be remembered.” “The new
heavens and the new earth shall remain before me.” “Let us
look, then, according to this promise, for the new heavens and
the new earth, wherein dwelleth righteousness.”—North-British
Review, No. 3.
Cuvier eloquently says: “It could not be expected that
those Phœnician sailors who saw the sand of the shores of
Bætica transformed by fire into a transparent Glass, should have
at once foreseen that this new substance would prolong the
pleasures of sight to the old; that it would one day assist the
astronomer in penetrating the depths of the heavens, and in
numbering the stars of the Milky Way; that it would lay open
to the naturalist a miniature world, as populous, as rich in
wonders as that which alone seemed to have been granted to
his senses and his contemplation: in fine, that the most simple
and direct use of it would enable the inhabitants of the coast
of the Baltic Sea to build palaces more magnificent than those
of Tyre and Memphis, and to cultivate, almost under the polar
circle, the most delicious fruit of the torrid zone.”
Galileo appears to be justly entitled to the honour of having
invented that form of Telescope which still bears his name;
while we must accord to John Lippershey, the spectacle-maker
of Middleburg, the honour of having previously invented the
astronomical telescope. The interest excited at Venice by
Galileo’s invention amounted almost to frenzy. On ascending
the tower of St. Mark, that he might use one of his telescopes
without molestation, Galileo was recognised by a crowd in the
street, who took possession of the wondrous tube, and detained
the impatient philosopher for several hours, till they had successively
witnessed its effects. These instruments were soon
manufactured in great numbers; but were purchased merely as
philosophical toys, and were carried by travellers into every
corner of Europe.
The moon displayed to him her mountain-ranges and her
glens, her continents and her highlands, now lying in darkness,
now brilliant with sunshine, and undergoing all those
variations of light and shadow which the surface of our own
globe presents to the alpine traveller or to the aeronaut. The
four satellites of Jupiter illuminating their planet, and suffering
eclipses in his shadow, like our own moon; the spots on
the sun’s disc, proving his rotation round his axis in twenty-five
days; the crescent phases of Venus, and the triple form
or the imperfectly developed ring of Saturn,—were the other
discoveries in the solar system which rewarded the diligence of
Galileo. In the starry heavens, too, thousands of new worlds
were discovered by his telescope; and the Pleiades alone, which
to the unassisted eye exhibit only seven stars, displayed to Galileo
no fewer than forty.—North-British Review, No. 3.
The first telescope “the starry Galileo” constructed with a leaden
tube a few inches long, with a spectacle-glass, one convex and one concave,
at each of its extremities. It magnified three times. Telescopes
were made in London in February 1610, a year after Galileo had completed
his own (Rigaud, On Harriot’s Papers, 1833). They were at first
called cylinders. The telescopes which Galileo constructed, and others
of which he made use for observing Jupiter’s satellites, the phases of
Venus, and the solar spots, possessed the gradually-increasing powers
of magnifying four, seven, and thirty-two linear diameters; but they
never had a higher power.—Arago, in the Annuaire for 1842.
Clock-work is now applied to the equatorial telescope, so as to allow
the observer to follow the course of any star, comet, or planet he may
wish to observe continuously, without using his hands for the mechanical
motion of the instrument.
Long tubes were certainly employed by Arabian astronomers,
and very probably also by the Greeks and Romans; the
exactness of their observations being in some degree attributable
to their causing the object to be seen through diopters or
slits. Abul Hassan speaks very distinctly of tubes, to the extremities
of which ocular and object diopters were attached;
and instruments so constructed were used in the observatory
founded by Hulagu at Meragha. If stars be more easily discovered
during twilight by means of tubes, and if a star be
sooner revealed to the naked eye through a tube than without
it, the reason lies, as Arago has truly observed, in the circumstance
that the tube conceals a great portion of the disturbing
light diffused in the atmospheric strata between the star and
the eye applied to the tube. In like manner, the tube prevents
the lateral impression of the faint light which the particles
of air receive at night from all the other stars in the
firmament. The intensity of the image and the size of the
star are apparently augmented.—Humboldt’s Cosmos, vol. iii.
p. 53.
The year 1668 may be regarded as the date of the invention
of Newton’s Reflecting Telescope. Five years previously, James
Gregory had described the manner of constructing a reflecting
telescope with two concave specula; but Newton perceived the
disadvantages to be so great, that, according to his statement,
he “found it necessary, before attempting any thing in the
practice, to alter the design, and place the eye-glass at the side
of the tube rather than at the middle.” On this improved
principle Newton constructed his telescope, which was examined
by Charles II.; it was presented to the Royal Society
near the end of 1671, and is carefully preserved by that distinguished
body, with the inscription:
“The first Reflecting Telescope; invented by Sir Isaac Newton,
and made with his own hands.”
Sir David Brewster describes this telescope as consisting of
a concave metallic speculum, the radius of curvature of which
was 12-2/3 or 13 inches, so that “it collected the sun’s rays at
the distance of 6-1/3 inches.” The rays reflected by the speculum
were received upon a plane metallic speculum inclined 45°
to the axis of the tube, so as to reflect them to the side of the
tube in which there was an aperture to receive a small tube
with a plano-convex eye-glass whose radius was one-twelfth
of an inch, by means of which the image formed by the speculum
was magnified 38 times. Such was the first reflecting
telescope applied to the heavens; but Sir David Brewster describes
this instrument as small and ill-made; and fifty years
elapsed before telescopes of the Newtonian form became useful
in astronomy.
The plan of this Telescope was intimated by Herschel,
through Sir Joseph Banks, to George III., who offered to defray
the whole expense of it; a noble act of liberality, which
has never been imitated by any other British sovereign. Towards
the close of 1785, accordingly, Herschel began to construct his
reflecting telescope, forty feet in length, and having a speculum
fully four feet in diameter. The thickness of the speculum,
which was uniform in every part, was 3½ inches, and its weight
nearly 2118 pounds; the metal being composed of 32 copper,
and 10·7 of tin: it was the third speculum cast, the two previous
attempts having failed. The speculum, when not in use,
was preserved from damp by a tin cover, fitted upon a rim of
close-grained cloth. The tube of the telescope was 39 ft. 4 in.
long, and its width 4 ft. 10 in.; it was made of iron, and was
3000 lbs. lighter than if it had been made of wood. The observer
was seated in a suspended movable seat at the mouth
of the tube, and viewed the image of the object with a magnifying
lens or eye-piece. The focus of the speculum, or place
of the image, was within four inches of the lower side of the
mouth of the tube, and came forward into the air, so that there
was space for part of the head above the eye, to prevent it
from intercepting many of the rays going from the object to
the mirror. The eye-piece moved in a tube carried by a slider
directed to the centre of the speculum, and fixed on an adjustible
foundation at the mouth of the tube. It was completed
on the 27th August 1789; and the very first moment it
was directed to the heavens, a new body was added to the
solar system, namely, Saturn and six of its satellites; and in
less than a month after, the seventh satellite of Saturn, “an
object,” says Sir John Herschel, “of a far higher order of
difficulty.”—Abridged from the North-British Review, No. 3.
This magnificent instrument stood on the lawn in the rear of Sir
William Herschel’s house at Slough; and some of our readers, like ourselves,
may remember its extraordinary aspect when seen from the
Bath coach-road, and the road to Windsor. The difficulty of managing
so large an instrument—requiring as it did two assistants in addition
to the observer himself and the person employed to note the time—prevented
its being much used. Sir John Herschel, in a letter to Mr.
Weld, states the entire cost of its construction, 4000l., was defrayed by
George III. In 1839, the woodwork of the telescope being decayed,
Sir John Herschel had it cleared away; and piers were erected, on
which the tube was placed, that being of iron, and so well preserved
that, although not more than one-twentieth of an inch thick, when in
the horizontal position it contained within all Sir John’s family; and
next the two reflectors, the polishing apparatus, and portions of the
machinery, to the amount of a great many tons. Sir John attributes
this great strength and resistance to the internal structure of the tube,
very similar to that patented under the name of corrugated iron-roping.
Sir John Herschel also thinks that system of triangular arrangement
of the woodwork was upon the principle to which “diagonal bracing”
owes its strength.
Sir David Brewster has remarked, that “the long interval
of half a century seems to be the period of hybernation during
which the telescopic mind rests from its labours in order to acquire
strength for some great achievement. Fifty years elapsed
between the dwarf telescope of Newton and the large instruments
of Hadley; other fifty years rolled on before Sir William
Herschel constructed his magnificent telescope; and fifty years
more passed away before the Earl of Rosse produced that colossal
instrument which has already achieved such brilliant discoveries.”25
In the improvement of the Reflecting Telescope, the first
object has always been to increase the magnifying power and
light by the construction of as large a mirror as possible; and
to this point Lord Rosse’s attention was directed as early as
1828, the field of operation being at his lordship’s seat, Birr
Castle at Parsonstown, about fifty miles west of Dublin. For
this high branch of scientific inquiry Lord Rosse was well fitted
by a rare combination of “talent to devise, patience to bear
disappointment, perseverance, profound mathematical knowledge,
mechanical skill, and uninterrupted leisure from other
pursuits;”26 all these, however, would not have been sufficient,
had not a great command of money been added; the gigantic
telescope we are about to describe having cost certainly not
less than twelve thousand pounds.
Lord Rosse ground and polished specula fifteen inches, two feet, and
three feet in diameter before he commenced the colossal instrument. It
is impossible here to detail the admirable contrivances and processes by
which he prepared himself for this great work. He first ascertained
the most useful combination of metals for specula, both in whiteness,
porosity, and hardness, to be copper and tin. Of this compound the reflector
was cast in pieces, which were fixed on a bed of zinc and copper,—a
species of brass which expanded in the same degree by heat as the
pieces of the speculum themselves. They were ground as one body to
a true surface, and then polished by machinery moved by a steam-engine.
The peculiarities of this mechanism were entirely Lord Rosse’s
invention, and the result of close calculation and observation: they were
chiefly, placing the speculum with the face upward, regulating the temperature
by having it immersed in water, usually at 55° Fahr., and regulating
the pressure and velocity. This was found to work a perfect
spherical figure in large surfaces with a degree of precision unattainable
by the hand; the polisher, by working above and upon the face of the
speculum, being enabled to examine the operation as it proceeded without
removing the speculum, which, when a ton weight, is no easy matter.
The contrivance for doing this is very beautiful. The machine is
placed in a room at the bottom of a high tower, in the successive floors
of which trap-doors can be opened. A mast is elevated on the top of the
tower, so that its summit is about ninety feet above the speculum. A
dial-plate is attached to the top of the mast, and a small plane speculum
and eye-piece, with proper adjustments, are so placed that the combination
becomes a Newtonian telescope, and the dial-plate the object.
The last and most important part of the process of working the speculum,
is to give it a true parabolic figure, that is, such a figure that each
portion of it should reflect the incident ray to the same focus. Lord
Rosse’s operations for this purpose consist—1st, of a stroke of the first
eccentric, which carries the polisher along one-third of the diameter of
the speculum; 2d, a transverse stroke twenty-one times slower, and
equal to 0·27 of the same diameter, measured on the edge of the tank,
or 1·7 beyond the centre of the polisher; 3d, a rotation of the speculum
performed in the same time as thirty-seven of the first strokes; and
4th, a rotation of the polisher in the same direction about sixteen times
slower. If these rules are attended to, the machine will give the true
parabolic figure to the speculum, whether it be six inches or three feet
in diameter. In the three-feet speculum, the figure is so true with the
whole aperture, that it is thrown out of focus by a motion of less than
the thirtieth of an inch, “and even with a single lens of one-eighth of
an inch focus, giving a power of 2592, the dots on a watch-dial are still
in some degree defined.”
Thus was executed the three-feet speculum for the twenty-six-feet
telescope placed upon the lawn at Parsonstown, which,
in 1840, showed with powers up to 1000 and even 1600; and
which resolved nebulæ into stars, and destroyed that symmetry
of form in globular nebulæ upon which was founded the hypothesis
of the gradual condensation of nebulous matter into suns
and planets.27
Scarcely was this instrument out of Lord Rosse’s hands,
when he resolved to attempt by the same processes to construct
another reflector, with a speculum six feet in diameter and fifty
feet long! and this magnificent instrument was completed early
in 1845. The focal length of the speculum is fifty-four feet. It
weighs four tons, and, with its supports, is seven times as heavy
as the four-feet speculum of Sir William Herschel. The speculum
is placed in one of the sides of a cubical wooden box, about
eight feet wide, and to the opposite end of this box is fastened
the tube, which is made of deal staves an inch thick, hooped
with iron clamp-rings, like a huge cask. It carries at its upper
end, and in the axis of the tube, a small oval speculum, six
inches in its lesser diameter.
The tube is about 50 feet long and 8 feet in diameter in
the middle, and furnished with diaphragms 6½ feet in aperture.
The late Dean of Ely walked through the tube with an umbrella
up.
The telescope is established between two lofty castellated
piers 60 feet high, and is raised to different altitudes by a
strong chain-cable attached to the top of the tube. This cable
passes over a pulley on a frame down to a windlass on the
ground, which is wrought by two assistants. To the frame are
attached chain-guys fastened to the counterweights; and the
telescope is balanced by these counterweights suspended by
chains, which are fixed to the sides of the tube and pass over
large iron pulleys. The immense mass of matter weighs about
twelve tons.
On the eastern pier is a strong semicircle of cast-iron, with
which the telescope is connected by a racked bar, with friction-rollers
attached to the tube by wheelwork, so that by
means of a handle near the eye-piece, the observer can move
the telescope along the bar on either side of the meridian, to
the distance of an hour for an equatorial star.
On the western pier are stairs and galleries. The observing
gallery is moved along a railway by means of wheels and a
winch; and the mechanism for raising the galleries to various
altitudes is very ingenious. Sometimes the galleries, filled with
observers, are suspended midway between the two piers, over
a chasm sixty feet deep.
An excellent description of this immense Telescope at
Birr Castle will be found in Mr. Weld’s volume of Vacation
Rambles.
Sir David Brewster thus eloquently sketches the powers of
the telescope at the close of his able description of the instrument,
which we have in part quoted from his Life of Sir Isaac
Newton.
We have, in the mornings, walked again and again, and ever with
new delight, along its mystic tube, and at midnight, with its distinguished
architect, pondered over the marvellous sights which it dis-closes,—the
satellites and belts and rings of Saturn,—the old and new
ring, which is advancing with its crest of waters to the body of the
planet,—the rocks, and mountains, and valleys, and extinct volcanoes
of the moon,—the crescent of Venus, with its mountainous outline,—the
systems of double and triple stars,—the nebulæ and starry clusters
of every variety of shape,—and those spiral nebular formations which
baffle human comprehension, and constitute the greatest achievement
in modern discovery.
The Astronomer Royal, Mr. Airy, alludes to the impression
made by the enormous light of the telescope,—partly by the
modifications produced in the appearance of nebulæ already
figured, partly by the great number of stars seen at a distance
from the Milky Way, and partly from the prodigious brilliancy
of Saturn. The account given by another astronomer of the
appearance of Jupiter was that it resembled a coach-lamp in
the telescope; and this well expresses the blaze of light which
is seen in the instrument.
The Rev. Dr. Scoresby thus records the results of his visits:
The range opened to us by the great telescope at Birr Castle is best,
perhaps, apprehended by the now usual measurement—not of distances
in miles, or millions of miles, or diameters of the earth’s orbit, but—of
the progress of light in free space. The determination within, no
doubt, a small proportion of error of the parallax of a considerable
number of the fixed stars yields, according to Mr. Peters, a space betwixt
us and the fixed stars of the smallest magnitude, the sixth, ordinarily
visible to the naked eye, of 130 years in the flight of light. This
information enables us, on the principles of sounding the heavens, suggested
by Sir W. Herschel, with the photometrical researches on the
stars of Dr. Wollaston and others, to carry the estimation of distances,
and that by no means on vague assumption, to the limits of space
opened out by the most effective telescopes. And from the guidance
thus afforded us as to the comparative power of the six feet speculum
in the penetration of space as already elucidated, we might fairly assume
the fact, that if any other telescope now in use could follow the
sun if removed to the remotest visible position, or till its light would
require 10,000 years to reach us, the grand instrument at Parsonstown
would follow it so far that from 20,000 to 25,000 years would be spent in
the transmission of its light to the earth. But in the cases of clusters
of stars, and of nebulæ exhibiting a mere speck of misty luminosity,
from the combined light of perhaps hundreds of thousands of suns, the
penetration into space, compared with the results of ordinary vision,
must be enormous; so that it would not be difficult to show the probability
that a million of years, in flight of light, would be requisite, in
regard to the most distant, to trace the enormous interval.
Hooke is said to have proposed the use of Telescopes having
a length of upwards of 10,000 feet (or nearly two miles), in
order to see animals in the moon! an extravagant expectation
which Auzout considered it necessary to refute. The Capuchin
monk Schyrle von Rheita, who was well versed in optics, had
already spoken of the speedy practicability of constructing telescopes
that should magnify 4000 times, by means of which
the lunar mountains might be accurately laid down.
Optical instruments of such enormous focal lengths remind
us of the Arabian contrivances of measurement: quadrants with
a radius of about 190 feet, upon whose graduated limb the
image of the sun was received as in the gnomon, through a
small round aperture. Such a quadrant was erected at Samarcand,
probably constructed after the model of the older
sextants of Alchokandi, which were about sixty feet in height.
A writer in the North-British Review, No. 50, considers it
strange that a variety of facts which must have presented
themselves to the most careless observer should not have led
to the earlier construction of Optical Instruments. The ancients,
doubtless, must have formed metallic articles with concave
surfaces, in which the observer could not fail to see himself
magnified; and if the radius of the concavity exceeded
twelve inches, twice the focal distance of his eye, he had in
his hands an extempore reflecting telescope of the Newtonian
form, in which the concave metal was the speculum, and his
eye the eye-glass, and which would magnify and bring near him
the image of objects nearly behind him. Through the spherical
drops of water suspended before his eye, an attentive observer
might have seen magnified some minute body placed
accidentally in its anterior focus; and in the eyes of fishes and
quadrupeds which he used for his food, he might have seen,
and might have extracted, the beautiful lenses which they
contain, and which he could not fail to regard as the principal
agents in the vision of the animals to which they belonged.
Curiosity might have prompted him to look through these remarkable
lenses or spheres; and had he placed the lens of the
smallest minnow, or that of the bird, the sheep, or the ox, in
or before a circular aperture, he would have produced a microscope
or microscopes of excellent quality and different magnifying
powers. No such observations seem, however, to have
been made; and even after the invention of glass, and its conversion
into globular vessels, through which, when filled with
any fluid, objects are magnified, the microscope remained undiscovered.
It is a remarkable fact in the history of astronomy (says
Sir David Brewster), that three of its most distinguished professors
were contemporaries. Galileo was the contemporary
of Tycho during thirty-seven years, and of Kepler during the
fifty-nine years of his life. Galileo was born seven years before
Kepler, and survived him nearly the same time. We have not
learned that the intellectual triumvirate of the age enjoyed
any opportunity for mutual congratulation. What a privilege
would it have been to have contrasted the aristocratic dignity
of Tycho with the reckless ease of Kepler, and the manly and
impetuous mien of the Italian sage!—Brewster’s Life of Newton.
At about the same time that Goodricke discovered the
variation of the remarkable periodical star Algol, or β Persei,
one Palitzch, a farmer of Prolitz, near Dresden,—a peasant by
station, an astronomer by nature,—from his familiar acquaintance
with the aspect of the heavens, was led to notice, among
so many thousand stars, Algol, as distinguished from the rest
by its variation, and ascertained its period. The same Palitzch
was also the first to re-discover the predicted comet of Halley
in 1759, which he saw nearly a month before any of the astronomers,
who, armed with their telescopes, were anxiously
watching its return. These anecdotes carry us back to the era
of the Chaldean shepherds.—Sir John Herschel’s Outlines.
Lord Macclesfield, the eminent mathematician, who was
twelve years President of the Royal Society, built at his seat,
Shirburn Castle in Oxfordshire, an Observatory, about 1739.
It stood 100 yards south from the castle-gate, and consisted of
a bed-chamber, a room for the transit, and the third for a mural
quadrant. In the possession of the Royal Astronomical Society
is a curious print representing two of Lord Macclesfield’s
servants taking observations in the Shirburn observatory; they
are Thomas Phelps, aged 82, who, from being a stable-boy to
Lord-Chancellor Macclesfield, rose by his merit and genius to
be appointed observer. His companion is John Bartlett, originally
a shepherd, in which station he, by books and observation,
acquired such a knowledge in computation, and of the
heavenly bodies, as to induce Lord Macclesfield to appoint
him assistant-observer in his observatory. Phelps was the
person who, on December 23d, 1743, discovered the great
comet, and made the first observation of it; an account of
which is entered in the Philosophical Transactions, but not the
name of the observer.
Lacaille, who made more observations than all his contemporaries
put together, and whose researches will have the
highest value as long as astronomy is cultivated, had an observatory
at the Collège Mazarin, part of which is now the
Palace of the Institute, at Paris.
For a long time it had been without observer or instruments; under
Napoleon’s reign it was demolished. Lacaille never used to illuminate
the wires of his instruments. The inner part of his observatory was
painted black; he admitted only the faintest light, to enable him to
see his pendulum and his paper: his left eye was devoted to the service
of looking to the pendulum, whilst his right eye was kept shut. The
latter was only employed to look to the telescope, and during the time
of observation never opened but for this purpose. Thus the faintest
light made him distinguish the wires, and he very seldom felt the necessity
of illuminating them. Part of these blackened walls were visible
long after the demolition of the observatory, which took place somewhat
about 1811.—Professor Mohl.
In the Edinburgh Review, 1850, we find the following illustrations
of the enormous propagation of minute errors:
The rod used in measuring a base-line is commonly about ten feet
long; and the astronomer may be said truly to apply that very rod to
mete the distance of the stars. An error in placing a fine dot which
fixes the length of the rod, amounting to one-five-thousandth of an inch
(the thickness of a single silken fibre), will amount to an error of 70
feet in the earth’s diameter, of 316 miles in the sun’s distance, and to
65,200,000 miles in that of the nearest fixed star. Secondly, as the
astronomer in his observatory has nothing further to do with ascertaining
lengths or distances, except by calculation, his whole skill and artifice
are exhausted in the measurement of angles; for by these alone
spaces inaccessible can be compared. Happily, a ray of light is straight:
were it not so (in celestial spaces at least), there would be an end of
our astronomy. Now an angle of a second (3600 to a degree) is a subtle
thing. It has an apparent breadth utterly invisible to the unassisted
eye, unless accompanied with so intense a splendour (e. g. in the case of
a fixed star) as actually to raise by its effect on the nerve of sight a
spurious image having a sensible breadth. A silkworm’s fibre, such as
we have mentioned above, subtends an angle of a second at 3½ feet
distance; a cricket-ball, 2½ inches diameter, must be removed, in order
to subtend a second, to 43,000 feet, or about 8 miles, where it would
be utterly invisible to the sharpest sight aided even by a telescope of
some power. Yet it is on the measure of one single second that the
ascertainment of a sensible parallax in any fixed star depends; and an
error of one-thousandth of that amount (a quantity still unmeasurable
by the most perfect of our instruments) would place the star too far or
too near by 200,000,000,000 miles; a space which light requires 118 days
to travel.
Aristotle maintains that Stars may occasionally be seen in
the Daylight, from caverns and cisterns, as through tubes.
Pliny alludes to the same circumstance, and mentions that
stars have been most distinctly recognised during solar eclipses.
Sir John Herschel has heard it stated by a celebrated optician,
that his attention was first drawn to astronomy by the regular
appearance, at a certain hour, for several successive days, of a
considerable star through the shaft of a chimney. The chimney-sweepers
who have been questioned upon this subject agree
tolerably well in stating that “they have never seen stars by
day, but that when observed at night through deep shafts, the
sky appeared quite near, and the stars larger.” Saussure states
that stars have been seen with the naked eye in broad daylight,
on the declivity of Mont Blanc, at an elevation of 12,757
feet, as he was assured by several of the alpine guides. The
observer must be placed entirely in the shade, and have a thick
and massive shade above his head, else the stronger light of
the air will disperse the faint image of the stars; these conditions
resembling those presented by the cisterns of the ancients,
and the chimneys above referred to. Humboldt, however,
questions the accuracy of these evidences, adding that in the
Cordilleras of Mexico, Quito, and Peru, at elevations of 15,000
or 16,000 feet above the sea-level, he never could distinguish
stars by daylight. Yet, under the ethereally pure sky of Cumana,
in the plains near the sea-shore, Humboldt has frequently
been able, after observing an eclipse of Jupiter’s satellites,
to find the planet again with the naked eye, and has
most distinctly seen it when the sun’s disc was from 18° to 20°
above the horizon.
By the nature of our atmosphere, we are protected from
the influence of the full flood of solar heat. The absorption
of caloric by the air has been calculated at about one-fifth of
the whole in passing through a column of 6000 feet, estimated
near the earth’s surface. And we are enabled, knowing the
increasing rarity of the upper regions of our gaseous envelope,
in which the absorption is constantly diminishing, to prove
that about one-third of the solar heat is lost by vertical transmission
through the whole extent of our atmosphere.—J. D.
Forbes, F.R.S.; Bakerian Lecture, 1842.
Soon after the completion of the Monument on Fish Street
Hill, by Wren, in 1677, it was used by Hooke and other members
of the Royal Society for astronomical purposes, but abandoned
on account of the vibrations being too great for the
nicety required in their observations. Hence arose the report
that the Monument was unsafe, which has been revived in our
time; “but,” says Elmes, “its scientific construction may bid
defiance to the attacks of all but earthquakes for centuries to
come.” This vibration in lofty columns is not uncommon.
Captain Smythe, in his Cycle of Celestial Objects, tells us, that
when taking observations on the summit of Pompey’s Pillar,
near Alexandria, the mercury was sensibly affected by tremor,
although the pillar is a solid.
