Herschel, John F. W. (John Frederick William), Sir, 1792-1871 · London : Longman, Rees Orme · leaf 105
nstruction ofthe instrument, at right angles, the great circles, whichare their vanishing lines, must be so too. Now, if twogreat circles of a sphere be at right angles to each other,the one will always pass through the others poles. (149.) There are, however, hut two positions inwhich such an… … CHAP. II. EQUATORIAL. 99 the vanishing points of all lines in this system of pa-rallels ; and when, of course, the plane of the circleA B is parallel to the earths equator, and therefore hasthe equinoctial for its vanishing circle, and measures,by its arcs read off, hour angles, or differences of…
Astronomy
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