[CHAPTER XXIII.]
Optics.
[Early Telescopes]—[The Lick Telescope]—[The Grande Lunette]—[The Stereo-Binocular Field Glass]—[The Microscope]—[The Spectroscope]—[Polarization of Light]—[Kaleidoscope]—[Stereoscope]—[Range Finder]—[Kinetoscope and Moving Pictures].
“And God said, Let there be light: and there was light. And God saw the light that it was good; and God divided the light from the darkness.” Thus early in the account of the creation is evidenced man’s appreciation of the value of vision. Of all the senses which place man in intelligent relation to his environment none is so important as sight. More than all the others does it establish our relation to the material world. When the babe is born, and its little emancipated soul is brought in contact with the world, its wondering gaze sees the panorama of visible things touching its eyes, and it stretches forth its tiny arms in the vain effort to pluck the stars, apparently within its reach. Distance and time add their values to light and vision, and as his life expands to greater fullness, the perspective of his existence creeps into his consciousness, and he finds himself farther away, but still peering beyond into the infinity of distance, searching for the visible evidence of knowledge. From the earliest times man learned to spurn the groveling things of earth, and to delight his soul with the marvelous infinity of the sky and its heavenly bodies. Nunc ad astra was his ambitious cry, and in no field has his quest for knowledge been more skillfully directed, faithfully maintained, or richly rewarded than in the study of astronomy. Many important discoveries in this field have been made in the Nineteenth Century, among which may be named the discovery of the planet Neptune by Adams, Leverrier and Galle in 1846; the satellites of Neptune in 1846, and those of Saturn in 1848 by Mr. Lassell; the two satellites of Mars by Prof. Asaph Hall in 1877; and the discovery of the so-called canals of Mars by Schiaparelli in 1877. But the purpose of this work is to deal with material inventions rather than scientific discoveries, and the leading invention in optics is the telescope.
Who invented the telescope is a question that cannot now be answered. For many years Galileo was credited in popular estimation with having made this invention in 1609. But it is now known that, while he built telescopes, and discovered the mountains of the moon, the spots on the sun’s disk, the crescent phases of Venus, the four satellites of Jupiter, the rings of Saturn, and made the first important astronomical observations, the invention of the telescope, as an instrument, could not be rightly claimed for him. Borelli credits it to Jansen & Lippersheim, spectacle makers, of Middelburg, Holland, about 1590; Descartes credits it to James Metius; Humboldt says Hans Lippershey (or Laprey), a native of Wesel and a spectacle maker of Middelburg in 1608, naming also Jacob Adriansz, sometimes called Metius and also Zacharias Jansen.
The great impetus given to the study of astronomy by Galileo, in 1609, was followed up by Huygens in 1655 with his improvement, by Gregory’s reflecting telescope of 1663, and Newton’s in 1668. In 1733 Chester More Hall invented the achromatic object glass of crown and flint glass. In 1758 John Dolland reinvented and introduced the same in the manufacture of telescopes. In 1779 Herschel built his reflecting telescope, and in March, 1781, he discovered the planet Uranus. In 1789 he built his great reflector. It was while the latter telescope was exploring the heavens that the Nineteenth Century began, and in the early part of this century Herschel laid before the Royal Society a catalogue of many thousand nebulæ and clusters of stars. Among the great telescopes of the Nineteenth Century may be mentioned that made in London in 1802 for the observatory of Madrid, which cost £11,000; the great reflecting telescope of the Earl of Rosse, erected at Parsonstown, in Ireland, in 1842-45. This was 6 feet diameter, 54 feet focal length, and cost over £20,000; the magnificent equatorial telescopes set up at the National Observatories at Greenwich and Paris in 1860; Foucault’s reflecting telescope at Paris, 1862, whose mirror was 311⁄2 inches diameter, and focal length 173⁄4 feet; Mr. R. S. Newall’s telescope, set up at Gateshead by Cookes, of York, in 1870; object glass, 25 inches, tube, 30 feet; Mr. A. Ainslie Common’s reflecting telescope, Ealing, Middlesex, 1879, mirror, 371⁄2 inches diameter, tube, 20 feet; the telescope at the United States Observatory, at Washington, 1873, object glass, 26 inches, tube, 33 feet long; and the large refracting telescope by Howard Grubb, at Dublin, for Vienna, 1881.
FIG. 194.—TELESCOPE AT LICK OBSERVATORY.