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The success of this first experiment inspired Newton with fresh zeal, and though his mind was now occupied with his optical discoveries, with the elements of his method of fluxions, and with the expanding germ of his theory of universal gravitation, yet with all the ardour of youth he applied himself to the laborious operation of executing another reflecting telescope with his own hands. This instrument, which was better than the first, though it lay by him several years, excited some interest at Cambridge; and Sir Isaac himself informs us, that one of the fellows of Trinity College had completed a telescope of the same kind, which he considered as somewhat superior to his own. The existence of these telescopes having become known to the Royal Society, Newton was requested to send his instrument for examination to that learned body. He accordingly transmitted it to Mr. Oldenburg in December, 1671, and from this epoch his name began to acquire that celebrity by which it has been so peculiarly distinguished.
On the 11th of January, 1672, it was announced to the Royal Society that his reflecting telescope had been shown to the king, and had been examined by the president, Sir Robert Moray, Sir Paul Neale, Sir Christopher Wren, and Mr. Hook. These gentlemen entertained so high an opinion of it, that, in order to secure the honour of the contrivance to its author, they advised the inventor to send a drawing and description of it to Mr. Huygens at Paris. Mr. Oldenburg accordingly drew up a description of it in Latin, which, after being corrected by Mr. Newton, was transmitted to that eminent philosopher. This telescope, of which the annexed is an accurate drawing, is carefully preserved in the library of the Royal Society of London, with the following inscription :
“ Invented by Sir Isaac Newton and made with his own hands, 1671."
It does not appear that Newton executed any other reflecting telescopes than the two we have mentioned. He informs us that he repolished and greatly improved a fourteen-feet object-glass, executed by a London artist, and having proposed in 1678 to substitute glass reflectors in place of metallic specula, he tried to make a reflecting telescope on this principle four feet long, and with a magnifying power of 150. The glass was wrought by a London artist, and though it seemed well finished, yet, when it was quicksilvered on its convex side, it exhibited all over the glass innumerable inequalities, which gave an indistinctness to every object. He expresses, however, his conviction that nothing but good workmanship is wanting to perfect these telescopes, and he recommends their consideration “to the curious in figuring glasses.”
For a period of fifty years this recommendation excited no notice. At last Mr. James Short of Edinburgh, an artist of consummate skill, executed about the year 1730 no fewer than six reflecting telescopes with glass specula, three of fifteen inches, and three of nine inches in focal length. He found it extremely troublesome to give them a true figure with parallel surfaces; and several of them when finished turned out useless, in consequence of the veins which then appeared in the glass. Although these instruments performed remarkably well, yet the light was fainter than he expected, and from this cause, combined with the difficulty of finishing them, he afterward devoted his labours solely to those with metallic specula.
At a later period, in 1822, Mr. G. B. Airy of Trinity College, and one of the distinguished successors of Newton in the Lucasian chair, resumed the consideration of glass specula, and demonstrated that the aberration both of figure and of colour might be corrected in these instruments. Upon this ingenious principle Mr. Airy executed more than
one telescope, but though the result of the experiment was such as to excite hopes of ultimate success, yet the construction of such instruments is still a desideratum in practical science.
Such were the attempts which Sir Isaac Newton made to construct reflecting telescopes; but notwithstanding the success of his labours, neither the phi. losopher nor the practical optician seems to have had courage to pursue them. A London artist, indeed, undertook to imitate these instruments; but Sir Isaac informs us, that “he fell much short of what he had attained, as he afterward understood by discoursing with the under workmen he had employed.” After a long period of fifty years, John Hadley, Esq. of Essex, a Fellow of the Royal Society, began in 1719 or 1720 to execute a reflecting telescope. His scientific knowledge and his manual dexterity fitted him admirably for such a task, and, probably after many failures, he constructed two large telescopes about five feet three inches long, one of which, with a speculum six inches in diameter, was presented to the Royal Society in 1723. The celebrated Dr. Bradley and the Rev. Mr. Pound compared it with the great Huygenian refractor 123 feet long. It bore as high a magnifying power as the Huygenian telescope : it showed objects equally distinct, though not altogether so clear and bright, and it exhibited every celestial object that had been discovered by Huygens,—the five satellites of Saturn, the shadow of Jupiter's satellites on his disk, the black list in Saturn's ring, and the edge of his shadow cast on the ring. Encouraged and instructed by Mr. Hadley, Dr. Bradley began the construction of reflecting telescopes, and succeeded so well that he would have completed one of them, had he not been obliged to change his residence. Some time afterward he and the Honourable Samuel Molyneux undertook the task together at Kew, and attempted to execute specula about twenty-six inches in focal
length; but notwithstanding Dr. Bradley's former experience, and Mr. Hadley's frequent instructions, it was a long time before they succeeded. The first good instrument which they finished was in May, 1724. It was twenty-six inches in focal length; but they afterward completed a very large one of eight feet, the largest that had ever been made. The first of these instruments was afterward elegantly fitted up by Mr. Molyneux, and presented to his majesty John V. King of Portugal.
The great object of these two able astronomers was to reduce the method of making specula to such a degree of certainty that they could be manufactured for public sale. Mr. Hauksbee had indeed made a good one about three and a half feet long, and had proceeded to the execution of two others, one of six feet, and another of twelve feet in focal length; but Mr. Scarlet and Mr. Hearne, having received all the information which Mr. Molyneux had acquired, constructed them for public sale; and the reflecting telescope has ever since been an article of trade with every regular optician.
As Sir Isaac Newton was at this time President of the Royal Society, he had the high satisfaction of seeing his own invention become an instrument of public use, and of great advantage to science, and he no doubt felt the full influence of this triumph of his skill. Still, however, the reflecting telescope had not achieved any new discovery in the heavens. The latest accession to astronomy had been made by the ordinary refractors of Huygens, labouring under all the imperfections of coloured light; and this long pause in astronomical discovery seemed to indicate that man had carried to its farthest limits his power of penetrating into the depths of the universe. This, however, was only one of those stationary positions from which human genius takes a new and a loftier elevation. While the English optieians were thus practising the recent art of grinding