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We can, however, hardly regret that Newton failed to discover the achromatic objective, when we observe that it was in consequence of his deeming an achromatic objective to be impossible that he was led to the invention of the reflecting telescope.
In doing this we need not go through with the formation of the several membranes, humors, etc., but take the crystalline lens as the most curious and nicely arranged and adapted of all the parts, and as giving, moreover, a close parallel, in the end produced, to that produced by design, by a human designer, Dollond, in forming his achromatic object-glass.
He remembered the thing as a bald discovery, and without a touch of emotion. With all the achromatic clearness, the unromantic colourlessness of the early morning.... Yes. He had it now quite distinctly. There had been no overnight reading. He was in Love. The proposition jarred with some vague thing in his mind.
AUTOLYCUS. A ring-plain 23 miles in diameter, deviating considerably from circularity, W. of Archimedes, on the Mare Imbrium, or rather on that part of it termed the Palus Putredinis. Its floor, which contains an inconspicuous central mountain, is depressed some 4000 feet below the surrounding country. With a power of 150 on a 4 5/8 achromatic, Dr.
In the course of experiments on light, directed towards the perfecting of his achromatic lenses, Fraunhofer, by means of a slit and a telescope, made the surprising discovery that the solar spectrum is crossed, not by seven, but by thousands of obscure transverse streaks. Nor did he stop here.
His success, so far, and the extraordinary facilities for observation afforded by the Fraunhofer achromatic encouraged him to undertake, February 11, 1825, a review of the entire heavens down to 15° south of the celestial equator, which occupied more than two years, and yielded, from an examination of above 120,000 stars, a harvest of about 2,200 previously unnoticed composite objects.
The two telescopes, the reflector and the achromatic, inventions of the last century, permitted man to penetrate into the infinite grandeurs of the universe, to recognize, as far as such a thing is possible, its illimitable spaces, its measureless times; and a little later the achromatic microscope placed before his eyes the world of the infinitely small.
It is impossible to see these different images clearly at the same time, because each of them will render all the others indistinct. The achromatic object-glass, invented by Dollond, about 1750, obviates this difficulty, and brings all the rays to nearly the same focus.
Connected with these buildings are store-houses, a room for the master and crew of the attending vessels, and a signal-tower fifty feet high, at the top of which is a small observatory furnished with an excellent achromatic telescope, a flag-staff, and a copper signal-ball measuring eighteen feet in diameter.
One of the most curious things on the shallow parts of Huron is to sail or row over the submarine or sublacune mountains, and to feel giddy from fancy, for it is like being in a balloon, so pure and tintless is the water. It is, like Dolland's best telescopes, achromatic.
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