Herschel, John F. W. (John Frederick William), Sir, 1792-1871 · London : Longman, Brown, Green, Longmans, and Roberts · leaf 147
one attached to the fixed support which carries the principal axis, the other to an arm projecting from that axis. Both circles also are susceptible of being clamped, the clamps being at¬ tached to the same ultimate bearing with which the apparatus for reading off is connected. (183.) It is… … the vanishing line of all the planes parallel to the circle G H ; and these two planes being, by the construction of the instrument, at right angles, the great circles, which are their vanishing lines, must be so too. Now, if two great circles of a sphere be at right angles to each other, the one…
Astronomy
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