ब्राह्मस्फुटसिद्धान्त (ब्रह्मगुप्त - शून्य, कुट्टक, बीजगणित एवं सम्पूर्ण २१ अध्याय सान्वय सटीक)

340 BRAHMAGUPTA AND ASTRONOMICAL INSTRUMENTS
that it cuts the plane of the horizon at right angles,
and one of the poles of the equator is elevated above
the horizon conformably with the latitude of the
place; then the motions of all the circles round the
poles represent the motions of the universe.
After rectifying the meridian, if it be wished to
observe the Sun and Moon together, the outer secon-
dary of the ecliptic must be made to intersect the
ecliptic at the Sun's place for that time: and the
solstitial colure must be moved until the place of
intersection be opposite to the Sun. Both circles are
thus adjusted to their true places; or if any object but
the Sun, be observed, the colure is turned until the
object be seen in its proper place, on that secondary
referred to the ecliptic: the circle representing the
ecliptic being at the same time in the plane of the
true ecliptic and in its proper situation. Afterwards,
the inner secondary is turned towards the Moon (or to
any star intended to be observed), and the smaller
circle within it, bearing the two sights is turned, until
the Moon, (or to any star intended to be observed),
and the smaller circle within it, bearing the two sights,
is turned, until the Moon be seen in the line of the
apertures. The intersection of the secondary circle and
ecliptic is the place of the Moon in longitude: and the
arc of the secondary, between the aperture and the
ecliptic, is the latitude of the Moon on either side
(North or South). (From Colebrooke's Miscellaneous
Essays).
The same instrument, as described by Montucla from the
text of Ptolemy (1. 3. c. 2) consists of six circles: first a large
circle representing the meridian; next four circles united toge-
ther, representing the equator, ecliptic and two colures, and
turning within the first circle on the poles of the equator, lastly
a circle turning on the poles of the ecliptic, furnished with sights
and nearly touching, on its concave side, the circumference of
the ecliptic.
The armillary sphere described by the Arabian epitomiser,
differs, therefore; from Ptolemy's in omitting the equator and