Chapter V: Part 5

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.

THE POLE-STAR FOUR THOUSAND YEARS AGO.

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.

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.

CHANGE OF COLOUR IN THE STARS.

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.

DISTANCE OF THE NEAREST FIXED STAR FROM THE EARTH.

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.

LIGHT OF A STAR SIXTEENFOLD THAT OF THE SUN.

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.

DIVERSITIES OF THE PLANETS.

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._

GRAND RESULTS OF THE DISCOVERY OF JUPITER’S SATELLITES.

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.

WAS SATURN’S RING KNOWN TO THE ANCIENTS?

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.

TEMPERATURE OF THE PLANET MERCURY.

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.

SPECULATIONS ON VESTA AND PALLAS.

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.

IS THE PLANET MARS INHABITED?

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.

DISCOVERY OF THE PLANET NEPTUNE.

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.

MAGNITUDE OF COMETS.

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.

COMETS VISIBLE IN SUNSHINE--THE GREAT COMET OF 1843.

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]

THE MILKY WAY UNFATHOMABLE.

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.

DISTANCES OF NEBULÆ.

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.

INFINITE SPACE.

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.

ORIGIN OF OUR PLANETARY SYSTEM. THE NEBULAR HYPOTHESIS.[22]

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.

ORIGIN OF HEAT IN OUR SYSTEM.

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.

AN ASTRONOMER’S DREAM VERIFIED.

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.

FIRE-BALLS AND SHOOTING STARS.

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._

THEORY AND EXPERIENCE.

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.”

METEORITES FROM THE MOON.

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.

VAST SHOWER OF METEORS.

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.

IMMENSE METEORITE.

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.

NO FOSSIL METEORIC STONES.

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]

THE END OF OUR SYSTEM.

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.

BENEFITS OF GLASS TO MAN.

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.”

THE GALILEAN TELESCOPE.

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.

WHAT GALILEO FIRST SAW WITH HIS TELESCOPE.

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.

ANTIQUITY OF TELESCOPES.

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.

NEWTON’S FIRST REFLECTING TELESCOPE.

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.

SIR WILLIAM HERSCHEL’S GREAT TELESCOPE AT SLOUGH.

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.