The latter half of the eighteenth century furnishes a large catalogue of distinguished names, men of high scientific ability, and, for the most part, of the finest mathematical minds, by whose labors practical astronomy made vast advances, and the physical theory of the universe, as previously developed, was amply illustrated and confirmed. During this era lunar tables were constructed of sufficient accuracy to be employed to solve the great problem of the longitude at sea. This was the work of Mayer, for which his widow received the sum of £3000 from government; and since that period, the publication of such tables, showing the places of the sun and moon, with the distance of the later from certain fixed stars, for every three hours, three years in advance, has been a national object, contributing to the safety of navigators upon the trackless deep. The same period is also celebrated for the determination of the figure and magnitude of the earth, and for the great improvements made in instruments of observation. If the century opened with lustre derived from the physical demonstrations of Newton, it closed magnificently with the telescopic discoveries of Herschel, the wonderful resident by the stately battlements of Windsor, by whose mechanical skill and matchless industry new regions were added to our solar system, and views unfolded of the infinity of the firmament, and the character of its architecture, which eye had not seen or the mind conceived.
A work specially devoted to the life and labors of Herschel is a desideratum. It is not to the credit of the country, that the men who have headed its physical force upon the field of battle have enjoyed a larger measure of public admiration and gratitude, and found a more speedy chronicle, than those who have enlarged the field of thought, ministered to the intellectual gratification, and elevated the mental character of the community. Bradley had lain in his grave 70 years, Newton 104, and Flamstead 116, before their memory received its meed of justice from the hands of Rigaud, Brewster, and Baily; a slackness to be attributed to the want of a due national estimate of the value of science, rather than to the reluctance of those who were competent to do ample honor to their merits. Herschel still remains without a record of this kind, though the materials for it are abundant, and his claims undoubted. Born at Hanover, the son of a musician in comparatively humble life, but early a resident in England, he appeared first as a professor and teacher of music, but rapidly rose by his own unaided efforts to eminence as an optician and astronomer. Anxious to inspect for himself the sublime revelations of the heavens, but destitute of means to purchase a telescope of sufficient power for his purpose, he resolved to employ some previous knowledge of optics and mechanics in the construction of an instrument. The earliest, a five-foot reflector, was completed in 1774: but altogether he accomplished the construction of upward of five hundred specula of various sizes, selecting the best of them for his telescopes. After having established his fame by the discovery of a new planet, and fixed his residence at Slough, under the munificent patronage of George the Third, he completed the giant instrument that attracted travelers from all parts to the spot, and rendered it one of the most remarkable sites of the civilized world. The tube was forty feet long, the speculum four feet in diameter, three inches and a half thick in every part, and weighing nearly two tons. Its space-penetrating power was estimated at 192, that is, it could search into the depths of the firmament 192 times farther than the naked eye. We can form no adequate conception of this extent, but only feebly approximate to it. Sirius, a star of the first magnitude, is separated by an immeasurable distance from us. But stars of a far inferior order of magnitude are visible to the naked eye. These we may conclude to be bodies far more remote, and reasonably suppose the star which presents the faintest pencil of light to the eye to be at least twice or thrice the distance of Sirius. Yet onward, 192 times farther, the space-penetrating power of the telescope at Slough swept the heavens. It was completed in the year 1789, but the frame of the instrument becoming decayed, through exposure to the weather, it was taken down by Sir John Herschel in 1823.
It will be convenient here to notice a reflecting telescope of far greater magnitude and power, recently constructed by the Earl of Rosse, and now in use at the seat of that nobleman, Birr Castle, in Ireland. The mechanical difficulties involved in this work, the patience, perseverance, and talent required to overcome them—and the great expenditure necessarily incurred—render the successful completion of this instrument one of the most extraordinary accomplishments of modern times; and entitle its owner and projector, from first to last, to the admiration of his countrymen. When the mechanical skill and profound mathematical knowledge essential to produce such a work are duly considered, together with the years devoted to previous experimenting, and an outlay of upward of twelve thousand pounds, this telescope must be regarded as one of the most remarkable and splendid offerings ever laid upon the altar of science. The speculum has a diameter of six feet, and therefore an area of reflecting surface nearly four times greater than that of the Herschelian, and its weight approaches to four tons. The casting—a work of no ordinary interest and difficulty—took place on the 13th of April, 1842, at nine in the evening; and as the crucibles poured forth their glowing contents—a burning mass of fluid matter, hissing, heaving and pitching—for the moment almost every one was anxious and fearful of accident or failure but Lord Rosse, who was observed directing his men as collectedly as on one of the ordinary occurrences of life. The speculum has been formed into a telescope of fifty feet local length, and is established between two walls of castellated architecture, against one of which the tube bears when in the meridian. It is no slight triumph of ingenuity, that this enormous instrument may be moved about and regulated by one man’s arm with perfect ease and certainty.
To return to Herschel. No addition had been made of any new body to the universe since Cassini discovered a fifth satellite in the train of Saturn. Nearly a century had elapsed without any further progress of that kind. The solar system, including the planets, satellites, and Halley’s comet, consisted of eighteen bodies when Herschel turned his attention to astronomy; but, before his career of observation terminated, he increased the number to twenty-seven, thus making the system half as large again as he found it, as to the number of its constituents—a brilliant recompense, but not an over-payment, considering the immense expenditure of time, and toil, and care. A primary planet with six moons, and two more satellites about Saturn, composed the reward. It was on the 13th of March, 1781, that, turning a telescope of high magnifying power—though not his gigantic instrument—to the constellation Gemini, he perceived a cluster of stars at the foot of Castor, and one in particular, which sensibly increased in diameter, while the rest of the stars remained unaltered. Two nights afterward, its place was changed, which originated the idea of its being a cometary body; an opinion embraced upon the continent when attention was called to it, but soon dispelled by clear evidence of its planetary nature. The new planet was named after the reigning monarch by the discoverer, but received his own name from astronomers, which was finally exchanged for the Uranus of heathen mythology, the oldest of the gods, the fabled father of Saturn and the grandsire of Jupiter—referring to the position of the planet beyond the orbits of the bodies named after the latter. By this discovery, the extent of the system was at once doubled; for the path of the stranger lies as far beyond what had been deemed its extreme confine, as that limit is removed from the sun. The first moment of his “attack” upon Saturn, upon completing the forty-feet reflector, he saw a sixth satellite, and a seventh moon later. But Herschel realized his most surprising results, and derives his greatest glory, from the observation of the sidereal heavens. The resolution of nebulæ and the Milky Way into an infinite number of stars—the discovery of new nebulæ of various forms, from the light luminous cloud to the nebulous star—of double and multiple stars—of the smaller revolving round the greater in the binary systems: these were some of his revelations to the world, as night after night, from dewy eve till break of dawn, he gauged the firmament. Caroline Herschel was the constant partner of her brother in his laborious undertakings—submitting to the fatigues of night attendance—braving with him the inclemency of the weather—noting down his observations as they issued from his lips—and taking, as the best of all authorities reports, the rough manuscript to the cottage at the dawn of day, and producing a fair copy of the night’s work on the ensuing morning. He died in 1822; but she has survived to see the heir of his name recognized by the world as the heir also of his talents and fame. It was one of the conceptions of this remarkable man—as bold an idea as ever entered the human mind—that the whole solar system has a motion in space, and is advancing toward a point in the heavens near the star λ Herculis. The idea remains to be verified; but it is not altogether unsupported by evidence, and quite consistent with the analogies of the universe.
The nineteenth century commenced with a fresh ingathering of members into the planetary family. It had been deemed a matter of surprise that the immense interval of about 350 millions of miles between Mars and Jupiter should be void, when only spaces varying from 25 to 50 millions divide Mars, the Earth, and the inferior planets. Keppler had therefore started the conjecture that a planet would be discovered in the vast region between the two former bodies; and thus bring it into something like proportion with the spaces between the latter. This idea was confirmed by a curious relation discovered by Professor Bode, of Berlin, that the intervals between the orbits of any two planets is about twice as great as the inferior interval, and only half the superior one. Thus, the distance between Venus and the Earth is double that between Mercury and Venus, and the half of that between the Earth and Mars. Uranus had not been discovered when Bode arrived at this remarkable analogy, but the distance of that planet being found to correspond with the law, furnished a striking confirmation of its truth. The respective distances of the planets may be expressed by the following series of numbers, whose law of progression is evident.
| Mercury’s distance | = | 4 | ||
| Venus | 4 + 3·0 | = | 7 | |
| Earth | 4 + 3·2 | = | 10 | |
| Mars | 4 + 3·22 | = | 16 | |
| Jupiter | 4 + 3·24 | = | 52 | |
| Saturn | 4 + 3·25 | = | 100 | |
| Uranus | 4 + 3·26 | = | 196 |
The void in the series between Mars and Jupiter, so convinced the German astronomers of the existence of a planet to occupy it—which had hitherto escaped observation—that a systematic search for the concealed body was commenced. At Lilienthal, the residence of Schroeter, an association of twenty-four observers was formed in the year 1800, for the purpose of examining all the telescopic stars of the zodiac. The opening years of the century witnessed the anticipation substantially realized by the discovery of four planets—Ceres, Pallas, Juno, and Vesta, revolving round the sun, at a mean distance of one hundred millions of miles from Mars, so small as only to be telescopic objects. This discovery we owe to Piazzi, Olbers, and Harding. Some singular features—without parallel in the planetary system—such as their close contiguity, the intersection of their orbits, with their diminutive size—Vesta not being much larger than the Spanish peninsula—led to the surmise that these bodies are fragments of a planet, which once revolved in their mean path with a magnitude proportionate to that of its neighbors. The possibility of such a disruption cannot be denied—the revolution of the fragments round the sun would follow in obedience to the mechanical laws by which the system is governed: but the point is obviously one of those questions which must remain entirely hypothetical. Next to this addition to the system, the most remarkable astronomical occurrences of the present age are the November meteors, the renewed return of Halley’s comet, and the determination of the annual parallax of the star 61 Cygni by Bessel. These will come under consideration in future pages, with the important contributions made to science by the great names of the day, Sir John Herschel, Sir James South, Struve, Airy, Arago, and others.
The progress of Astronomical discovery which has now been hastily traced, reminds us of the obligations we owe to those who have gone before us. While supplied with views respecting the constitution of the solar universe—the number, forms, magnitudes, distances, and movements of its members—upon the general accuracy of which the mind may repose with full satisfaction, the mode of its formation has been grappled with, and a theory presented, derived from the study of the sidereal heavens, which—though not demonstrable—is invested with a high degree of probability. The firmament exhibits dimly luminous appearances, like patches of white cloud, displaying various forms and peculiarities of structure, which are not resolvable into closely packed clusters of stars by any telescopic power, and whose phases are at variance with the idea that they are stellar groups, indistinct and blended from their remoteness. The nebulous substance, in one of its states, is evenly diffused, resembling a sheet of fog. Under another aspect, it is seen winding, and we detect a tendency toward structure, in the material congregating in different places, as if under the influence of a law of attraction. Definite structure appears in other cases, generally the spherical form, with great condensation at the centre, like regular stars in the midst of a thick haze. The question has hence naturally arisen, and it is one of profound interest—What do such appearances indicate? What do the differences in their character portend? Are they void and unmeaning substances in a universe of organization and order; or, are they advancing by a principle of progressive formation to share themselves in that order and organization? The idea has been started that, in these phenomena, we have an exhibition of the first state of the now organized bodies of our system, and of their progress to the ultimate conditions of their being, passing from one stage of construction to another, under control of the law of gravitation. This is substantially the nebular hypothesis of Laplace and Herschel: it supposes a diffused nebulosity, rotating with the solar nucleus, and extending beyond the bounds of the farthest planet, to have gradually condensed at the surface of the nucleus, accelerating thereby the solar rotation, and increasing the centrifugal force, by the action of which successive zones were detached, assuming spheroidal masses by the mutual attraction of their particles. This theory enlists a variety of evidence in its behalf. The fact of the projectile motions of all the planets and satellites taking place from west to east, in nearly the same plane—of their axical rotation likewise being all in the same direction, and corresponding with that of the solar body—is an instance of coincidence so extraordinary as strongly to support the theory of their common origin in obedience to a common law. It is no unimportant consideration that, in the physical and mental constitution of our own nature—with reference also to the inferior animals, both the feeble and the powerful, the tractable and the untamed—in relation too to the vegetable productions of the earth, whether flourishing in green savannas, or rooted in the clefts of the rock—we have a law of gradual formation now operating, which vindicates the idea from the charge of vain conceit, that an analogical law has operated with reference to the earth itself, and the various worlds that compose our system, supported—as the hypothesis is—by such significant evidences as the nebulous appearances in the heavens.
From the view which has now been taken, it is evidently no doubtful point to us—
“Whether the sun, predominant in heaven,