File:The elements of astronomy; a textbook (1919) (14595642418).jpg

Identifier: elementsofastro00youn (find matches)
Title: The elements of astronomy; a textbook
Year: 1919 (1910s)
Authors: Young, Charles A. (Charles Augustus), 1834-1908 Young, Anne Sewell, b. 1871., ed
Subjects: Astronomy Constellations
Publisher: Boston, New York (etc.) Ginn and Company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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n 1842, and still used. One still larger, 100 inches in diameter,was mounted in 1917 at the Carnegie Solar Observatory on Mt.Wilson, where a five-foot reflector was mounted in 1908. Anotherfive-foot reflector, made by Mr. Common, in England, in 1889, wasacquired by the Harvard College Observatory in 1905. The Crossleyreflector at the Lick Observatory, with which Keeler made his won-derful photographs, has an aperture of three feet. Of the refractors, the largest is that of the Yerkes Observatory, ofthe Chicago University. It has an aperture of 40 inches-and a focaL 408 APPENDIX. (§538 length of 6 5 feet. Next follows that of the Lick Observatory (see Fron-tispiece), which has a diameter of 36 inches and a length of 57 feet.The next in size is the 32-inch (visual) telescope at Meudon, whichis followed by the Potsdam telescope, SI J inches in diameter; andthis is nearly equalled by the telescopes at Pulkowa, Nice, Alleghenyand Paris (291 to 30 inches). Then come the new Greenwich tele-
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FlG. 146. — The Melbourne Reflector. Scope, 28 inches ; the Vienna telescope, 27 inches ; the two telescopesat Washington and the University of Virginia, 26i inches ; and theNewall telescope (lately presented to the University of Cambridge,England), 25 inches. This list includes most of the refractors whichhave an aperture exceeding two feet, but a number of others are now § 538) REFLECTORS VS. REFRACTORS. 409 under construction. The two largest of these object-glasses, andthose of the Pulkowa, Washington, and University of Virginia tele-scopes, were made by the Clarks, as well as the 24-inch telescope ofthe Lowell Observatory and the 23-inch instrument at Princeton. 539. Relative Advantages of Reflectors and Refractors.— There is much earnest discussion on this point, each form ofinstrument having its earnest partisans. In favor of the reflec-tors we may mention 1. Ease of construction and cheapness: the speculum has butone surface to be worked, while the object-glass has four o

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