File:A high-school astronomy- in which the descriptive, physical, and practical are combined (1859) (14764245195).jpg

Identifier: highschoolastro00matt (find matches)
Title: A high-school astronomy: in which the descriptive, physical, and practical are combined ..
Year: 1859 (1850s)
Authors: Mattison, Hiram, 1811-1868
Subjects: Astronomy
Publisher: New York, Mason brothers
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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t on the 13th of April,1842, and was cooled gradually in an oven for 16 weeks,to prevent its cracking, by a sudden or unequal reduc-tion of the temperature. This speculum has a reflectingsurface of 4,071 square inches. The tube is made ofdeal wood, one inch thick, and hooped with iron. Itsdiameter is seven feet, and its length 56. The entire weight of this telescope is twelve tons.It is mounted between two north and south walls, 24 feetapart, 72 feet long, and 48 feet high. The lower endrests upon a universal hinge. It can be lowered to thehorizon, and raised to the zenith, and lowered northwardtill it takes in the Pole star. Its motion from east towest is limited to 15 degrees. This magnificent instru-ment is situated at Burr Castle, Ireland. It was con-structed by the Earl of Rosse, at an expense of $60,000. 537. Lord Kosses telescope ? Weight of speculum ? Diameter? Thick-ness ? Cooling ? Tube ? Entire weight ? How mounted ? What motion ?Where located? Cost? TRANSIT INSTRUMENT. 235
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TRANSIT INSTRUMENT. 538, A Transit Instrument is a telescope used for ob-serving the transit of celestial objects across the meri-dian, for the purpose of determining differences of rightascension, or obtaining correct time. They are usuallyfrom six to ten feet long, and are mounted upon a hori-zontal axis, between two abutments of mason work; sothat the instrument, when horizontal, will point exactlyto the south. It will then take objects in the heavens,when they are exactly on the meridian. Let A D in the cut represent the telescope, and E and W the east and west abutments,between which it is placed. On the left is seen, attached to the mason work, a gradu-ated circle; and on the eastern end of the axis of the telescope is seen an arm, n, ex-tending to the circle, as an index. Now, suppose the index n to be at o, in the upperpart of the circle, when the telescope is horizontal; then if the meridian altitude of theobject to be taken is 10°, the index must be moved 10° from o, as th

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