In a qualified though very real sense, Sir William Herschel may be called the Founder of Sidereal Astronomy. Before his time some curious facts had been noted, and some ingenious speculations hazarded, regarding the condition of the stars, but not even the rudiments of systematic knowledge had been acquired. The facts ascertained can be summed up in a very few sentences.
Giordano Bruno was the first to set the suns of space in motion; but in imagination only. His daring surmise was, however, confirmed in 1718, when Halley announced[3] that Sirius, Aldebaran, Betelgeux, and Arcturus had unmistakably shifted their quarters in the sky since Ptolemy assigned their places in his catalogue. A similar conclusion was reached by J. Cassini in 1738, from a comparison of his own observations with those made at Cayenne by Richer in 1672; and Tobias Mayer drew up in 1756 a list showing the direction and amount of about fifty-seven proper motions,[4] founded on star-places determined by Olaus Römer fifty years previously. Thus the stars were no longer regarded as "fixed," but the question remained whether the movements perceived were real or only apparent; and this it was not yet found possible to answer. Already, in the previous century, the ingenious Robert Hooke had suggested an "alteration of the very system of the sun,"[5] to account for certain suspected changes in stellar positions; Bradley in 1748, and Lambert in 1761, pointed out that such apparent displacements (by that time well ascertained) were in all probability a combined effect of motions both of sun and stars; and Mayer actually attempted the analysis, but without result.
On the 13th of August, 1596, David Fabricius, an unprofessional astronomer in East Friesland, saw in the neck of the Whale a star of the third magnitude, which by October had disappeared. It was, nevertheless, visible in 1603, when Bayer marked it in his catalogue with the Greek letter ο, and was watched, in 1638-39, through its phases of brightening and apparent extinction by a Dutch professor named Holwarda.[6] From Hevelius this first-known periodical star received the name of "Mira," or the Wonderful, and Boulliaud in 1667 fixed the length of its cycle of change at 334 days. It was not a solitary instance. A star in the Swan was perceived by Janson in 1600 to show fluctuations of light, and Montanari found in 1669 that Algol in Perseus shared the same peculiarity to a marked degree. Altogether the class embraced in 1782 half-a-dozen members. When it is added that a few star-couples had been noted in singularly, but it was supposed accidentally, close juxtaposition, and that the failure of repeated attempts to measure stellar parallaxes pointed to distances at least 400,000 times that of the earth from the sun,[7] the picture of sidereal science, when the last quarter of the eighteenth century began, is practically complete. It included three items of information: that the stars have motions, real or apparent; that they are immeasurably remote; and that a few shine with a periodically variable light. Nor were these scantily collected facts ordered into any promise of further development. They lay at once isolated and confused before the inquirer. They needed to be both multiplied and marshalled, and it seemed as if centuries of patient toil must elapse before any reliable conclusions could be derived from them. The sidereal world was thus the recognised domain of far-reaching speculations, which remained wholly uncramped by systematic research until Herschel entered upon his career as an observer of the heavens.
The greatest of modern astronomers was born at Hanover, November 15, 1738. He was the fourth child of Isaac Herschel, a hautboy-player in the band of the Hanoverian Guard, and was early trained to follow his father's profession. On the termination, however, of the disastrous campaign of 1757, his parents removed him from the regiment, there is reason to believe, in a somewhat unceremonious manner. Technically, indeed, he incurred the penalties of desertion, remitted—according to the Duke of Sussex's statement to Sir George Airy—by a formal pardon handed to him personally by George III. on his presentation in 1782.[8] At the age of nineteen, then, his military service having lasted four years, he came to England to seek his fortune. Of the life of struggle and privation which ensued little is known beyond the circumstances that in 1760 he was engaged in training the regimental band of the Durham Militia, and that in 1765 he was appointed organist at Halifax. In the following year he removed to Bath as oboist in Linley's orchestra, and in October 1767 was promoted to the post of organist in the Octagon Chapel. The tide of prosperity now began to flow for him. The most brilliant and modish society in England was at that time to be met at Bath, and the young Hanoverian quickly found himself a favourite and the fashion in it. Engagements multiplied upon him. He became director of the public concerts; he conducted oratorios, engaged singers, organised rehearsals, composed anthems, chants, choral services, besides undertaking private tuitions, at times amounting to thirty-five or even thirty-eight lessons a week. He in fact personified the musical activity of a place then eminently and energetically musical.
But these multifarious avocations did not take up the whole of his thoughts. His education, notwithstanding the poverty of his family, had not been neglected, and he had always greedily assimilated every kind of knowledge that came in his way. Now that he was a busy and a prosperous man, it might have been expected that he would run on in the deep professional groove laid down for him. On the contrary, his passion for learning seemed to increase with the diminution of the time available for its gratification. He studied Italian, Greek, mathematics; Maclaurin's Fluxions served to "unbend his mind"; Smith's Harmonics and Optics and Ferguson's Astronomy were the nightly companions of his pillow. What he read stimulated without satisfying his intellect. He desired not only to know, but to discover. In 1772 he hired a small telescope, and through it caught a preliminary glimpse of the rich and varied fields in which for so many years he was to expatiate. Henceforward the purpose of his life was fixed: it was to obtain "a knowledge of the construction of the heavens";[9] and this sublime ambition he cherished to the end.
A more powerful instrument was the first desideratum; and here his mechanical genius came to his aid. Having purchased the apparatus of a Quaker optician, he set about the manufacture of specula with a zeal which seemed to anticipate the wonders they were to disclose to him. It was not until fifteen years later that his grinding and polishing machines were invented, so the work had at that time to be entirely done by hand. During this tedious and laborious process (which could not be interrupted without injury, and lasted on one occasion sixteen hours), his strength was supported by morsels of food put into his mouth by his sister,[10] and his mind amused by her reading aloud to him the Arabian Nights, Don Quixote, or other light works. At length, after repeated failures, he found himself provided with a reflecting telescope—a 5-1/2-foot Gregorian—of his own construction. A copy of his first observation with it, on the great Nebula in Orion—an object of continual amazement and assiduous inquiry to him—is preserved by the Royal Society. It bears the date March 4, 1774.[11]
In the following year he executed his first "review of the heavens," memorable chiefly as an evidence of the grand and novel conceptions which already inspired him, and of the enthusiasm with which he delivered himself up to their guidance. Overwhelmed with professional engagements, he still contrived to snatch some moments for the stars; and between the acts at the theatre was often seen running from the harpsichord to his telescope, no doubt with that "uncommon precipitancy which accompanied all his actions."[12] He now rapidly increased the power and perfection of his telescopes. Mirrors of seven, ten, even twenty feet focal length, were successively completed, and unprecedented magnifying powers employed. His energy was unceasing, his perseverance indomitable. In the course of twenty-one years no less than 430 parabolic specula left his hands. He had entered upon his forty-second year when he sent his first paper to the Philosophical Transactions; yet during the ensuing thirty-nine years his contributions—many of them elaborate treatises—numbered sixty-nine, forming a series of extraordinary importance to the history of astronomy. As a mere explorer of the heavens his labours were prodigious. He discovered 2,500 nebulæ, 806 double stars, passed the whole firmament in review four several times, counted the stars in 3,400 "gauge-fields," and executed a photometric classification of the principal stars, founded on an elaborate (and the first systematically conducted) investigation of their relative brightness. He was as careful and patient as he was rapid; spared no time and omitted no precaution to secure accuracy in his observations; yet in one night he would examine, singly and attentively, up to 400 separate objects.
The discovery of Uranus was a mere incident of the scheme he had marked out for himself—a fruit, gathered as it were by the way. It formed, nevertheless, the turning-point in his career. From a star-gazing musician he was at once transformed into an eminent astronomer; he was relieved from the drudgery of a toilsome profession, and installed as Royal Astronomer, with a modest salary of £200 a year; funds were provided for the construction of the forty-foot reflector, from the great space-penetrating power of which he expected unheard-of revelations; in fine, his future work was not only rendered possible, but it was stamped as authoritative.[13] On Whit-Sunday 1782, William and Caroline Herschel played and sang in public for the last time in St. Margaret's Chapel, Bath; in August of the same year the household was moved to Datchet, near Windsor, and on April 3, 1786, to Slough. Here happiness and honours crowded on the fortunate discoverer. In 1788 he married Mary, only child of James Baldwin, a merchant of the city of London, and widow of Mr. John Pitt—a lady whose domestic virtues were enhanced by the possession of a large jointure. The fruit of their union was one son, of whose work—the worthy sequel of his father's—we shall have to speak further on. Herschel was created a Knight of the Hanoverian Guelphic Order in 1816, and in 1821 he became the first President of the Royal Astronomical Society, his son being its first Foreign Secretary. But his health had now for some years been failing, and on August 25, 1822, he died at Slough, in the eighty-fourth year of his age, and was buried in Upton churchyard.
His epitaph claims for him the lofty praise of having "burst the barriers of heaven." Let us see in what sense this is true.
The first to form any definite idea as to the constitution of the stellar system was Thomas Wright, the son of a carpenter living at Byer's Green, near Durham. With him originated what has been called the "Grindstone Theory" of the universe, which regarded the Milky Way as the projection on the sphere of a stratum or disc of stars (our sun occupying a position near the centre), similar in magnitude and distribution to the lucid orbs of the constellations.[14] He was followed by Kant,[15] who transcended the views of his predecessor by assigning to nebulæ the position they long continued to occupy, rather on imaginative than scientific grounds, of "island universes," external to, and co-equal with, the Galaxy. Johann Heinrich Lambert,[16] a tailor's apprentice from Mühlhausen, followed, but independently. The conceptions of this remarkable man were grandiose, his intuitions bold, his views on some points a singular anticipation of subsequent discoveries. The sidereal world presented itself to him as a hierarchy of systems, starting from the planetary scheme, rising to throngs of suns within the circuit of the Milky Way—the "ecliptic of the stars," as he phrased it—expanding to include groups of many Milky Ways; these again combining to form the unit of a higher order of assemblage, and so onwards and upwards until the mind reels and sinks before the immensity of the contemplated creations.