Items related to Manual of spherical and practical astronomy Volume...
Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1868 Excerpt: ...and its axis is not symmetrically supported, it is not suited to the accurate determination of right ascensions, and is to be regarded as designed solely for the measurement of declinations. Even for this purpose the meridian circle is preferable, as it admits of reversal; and there is always an advantage in combining determinations made in reverse positions of an instrument, whereby unknown errors may be either wholly or in part eliminated. I shall, therefore, not treat specially of the mural circle. It is not probable that any more instruments of that form will hereafter be constructed; and the method of using those that exist will readily be understood by any one who has mastered the meridian circle. 195. Plates VII., VIH., and IX. represent a meridian circle of Repsold, belonging to the U. S. Naval Academy, and mounted at Annapolis in 1852. It is almost identical in form with the meridian circles constructed by the same artist for Struve and Bessel at the Pulkowa and Kimigsberg Observatories. It has two circles, CC and C' C', of the same size, but only one of these, CC, is graduated finely; this is read by four microscopes, two of which are seen at RH. The microscopes are carried upon a square frame which is centred upon the rotation axis itself: the form of this frame is shown in Plate IX., where the instrument is represented upon the reversing car. The horizontal sides of the frame carry two spirit levels I, I, by which any change of inclination of the frame with respect to the horizon may be detected. The second circle C'C', constructed of the same size as the first for the sake of symmetry, is graduated more coarsely, is read at either of two points, and is used only as a finder. The counterpoises TFlTact at JTJT, points nearly equidistant between t...
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