The first was scarcely more than a reconnaissance. It was made in 1775, with a small reflector of the Newtonian make.[A] Its upshot was to impress him with the utter disproportion between his daring plans and the means as yet at his disposal. Speculum-casting accordingly recommenced with fresh vigour. Seven- and ten-foot mirrors were succeeded by others of twelve, and even of twenty feet focal length. The finishing of them was very laborious. It was at that time a manual process, during the course of which the hands could not be removed from the metal without injury to its figure. One stretch of such work lasted sixteen hours, Miss Herschel meantime, “by way of keeping him alive,” putting occasional morsels of food into the diligent polisher’s mouth. His mode of procedure was to cast and finish many mirrors of each sort; then to select the best by trial, and repolish the remainder. In this manner he made, before 1781, “not less than 200 seven-foot, 150 ten-foot, and about 80 twenty-foot mirrors, not to mention those of the Gregorian form.” Repolishing operations were, moreover, accompanied by constant improvements, so that each successive speculum tended to surpass its predecessors.
[A] In “Newtonian” telescopes the image formed by the large speculum is obliquely reflected from a small plane mirror to the side of the tube, where it is viewed with an ordinary eye-piece. With a “Gregorian,” the observer looks straight forward, the image being thrown back by a little concave mirror through a central perforation in the speculum where the eye-piece is fitted.
These absorbing occupations were interrupted by the unwelcome news that Dietrich, the youngest of the Herschel family, had decamped from Hanover “with a young idler” like himself. William instantly started for Holland, where the fugitive was supposed to be about to take ship for India, but missed his track; and, after having extended his journey to Hanover to comfort his anxious mother—his father had died in 1767—returned sadly to Bath. There, to his immense surprise, he found the scapegrace in strict charge of his sister, “who kept him to a diet of roasted apples and barley-water.” His ineffectual escapade had terminated with an attack of illness at Wapping, whither Alexander Herschel, on learning how matters stood, had posted off to take him in charge and watch his recovery. Musical occupation was easily procured for him at Bath, since he was an accomplished violinist—had, indeed, started on his unprosperous career in the guise of an infant prodigy; but he threw it up in 1779 and drifted back to Hanover, married a Miss Reif, and settled down to live out a fairly long term of shiftless, albeit harmless, existence.
In 1776 William Herschel succeeded Thomas Linley, Sheridan’s father-in-law, as Director of the Public Concerts at Bath. His duties in this capacity, while the season lasted, were most onerous. He had to engage performers, to appease discontents, to supply casual failures, to write glees and catches expressly adapted to the voices of his executants, frequently to come forward himself as a soloist on the hautboy or the harpsichord. The services of his brother Alexander, a renowned violoncellist, and of his sister, by this time an excellent singer, were now invaluable to him. Nor for musical purposes solely. The vision of the skies was never lost sight of, and the struggle to realise it in conjunction with his sympathetic helpers absorbed every remnant of time. At meals the only topics of conversation were mechanical devices for improving success and averting failure. William ate with a pencil in his hand, and a project in his head. Between the acts at the theatre, he might be seen running from the harpsichord to his telescope. After a rehearsal or a morning performance, he would dash off to the workshop in periwig and lace ruffles, and leave it but too often with those delicate adjuncts to his attire torn and pitch-bespattered. Accidents, too, menacing life and limb, were a consequence of that “uncommon precipitancy which accompanied all his actions;” but he escaped intact, save for the loss of a finger-nail.
His introduction to the learned world of Bath was thus described by himself:—
“About the latter end of December, 1779, I happened to be engaged in a series of observations on the lunar mountains; and the moon being in front of my house, late in the evening I brought my seven-feet reflector into the street, and directed it to the object of my observations. Whilst I was looking into the telescope, a gentleman, coming by the place where I was stationed, stopped to look at the instrument. When I took my eye off the telescope, he very politely asked if he might be permitted to look in, and this being immediately conceded, he expressed great satisfaction at the view.”
The inquisitive stranger called next morning, and proved to be Dr. (later Sir William) Watson. He formed on the spot an unalterable friendship for the moon-struck musician, and introduced him to a Philosophical Society which held its meetings at his father’s house. Herschel’s earliest essays were read before it, but they remained unpublished. His first printed composition appeared in the “Ladies’ Diary” for 1780. It was an answer to a prize question on the vibration of strings.
The long series of his communications to the Royal Society of London opened May 11th, 1780, with a discussion of his observations, begun in October, 1777, of Mira, the variable star in the neck of the Whale. As to the theory of its changes, he agreed with Keill that they could best be explained by supposing rotation on an axis to bring a lucid side and a side obscured by spots alternately into view. A second paper by him on the Mountains of the Moon was read on the same day. He measured, in all, about one hundred of these peaks and craters.
In January, 1781, there came an essay stamped with the peculiar impress of his genius, entitled “Astronomical Observations on the Rotation of the Planets round their Axes, made with a view to determine whether the earth’s diurnal motion is perfectly equable.” It embodied an attempt to apply a definite criterion to the time-keeping of our planet. But the prospect is exceedingly remote of rating one planet-clock by the other. Herschel’s methods of inquiry are, however, aptly illustrated in this curiously original paper. His speculations always invited the control of facts. If facts were not at hand, he tried somehow to collect them. The untrammelled play of fancy was no more to his mind than it was to Newton’s. His ardent scientific imagination was thus, by the sobriety of his reason, effectively enlisted in the cause of progress.
Herschel began in 1780 his second review of the heavens, using a seven-foot Newtonian, of 6¼ inches aperture, with a magnifying power of 227. “For distinctness of vision,” he said, “this instrument is, perhaps, equal to any that was ever made.” His praise was amply justified. As he worked his way with it through the constellation Gemini, on the night of March 13th, 1781, an unprecedented event occurred. “A new planet swam into his ken.” He did not recognise it as such. He could only be certain that it was not a fixed star. His keen eye, armed with a perfect telescope, discerned at once that the object had a disc; and the application of higher powers showed the disc to be a substantial reality. The stellar “patines of bright gold” will not stand this test. Being of purely optical production, they gain nothing by magnification.