An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

ASTIZONO.!fICA, I NS'rl-tM.U iCW'LS. 67
inclined to thle horizon, still it is their angular distance measured on thite /torizont whlicth determines their difl'eelnee of
azimnuth, lFitgure 18 represents an Altitude and Azimuth Instrumuent, several of t-h1 usual appendages and subordinate
contrivances being omitted for the sake of distinctness anld
simIplicity. Itere a7bc is the vertical or altitude circle, an(l IEt;
the horizontal or azitmuth circle; Ai3 is a telescope mounted
Fig. 1.8.
on a horizontal axis and capable of two motionll, one in alltitude parallel to thle circle abe, and the other iln azimutlh parallel
to JlFG. 1:fence it can be easily broughlt to bear upon ally
object. At i, mIunder tlhe ee-glass of the tele>scope, is a smaall
mitror placed at an areglr of 4,:50 witflt the axis of the telescope,
by melans of wttich the image of the object is reflected upward, so as to be conveniently presented to the eye of tlle observer. A.t ( is represented a. tanuzgent sorew, by which a slow
motion is given to the teleseope at c. At It and g are seen two
spritd-levet.s at right alngles to cachl other, wlichl sllow \wNhenl the
azimuth circle is truly horizontal. Tllc instrument is supplortcd
on a tlJitpod, for the sake of greaterl steadiness, eacll foot being
fulrliscled witht a scre-w for leveling.