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

336 BRAHMAGUPTA AND ASTRONOMICAL INSTRUMENTS
have continuous flow. Where the water falling on
the ground spreads in a circle, there the ground is in
perfect level; where the water accumulates after
departing from the circle of water, it is low; and where
the water does not reach, there it is high. (Bhāskara's
Commentary on the Āryabhaṭīya, II. 13).
After the ground was levelled, a prominently distinct circle
was drawn on the ground as stated in the text (MBh. III. 1).
In the time of Śaṅkaranārāyaṇa (869 A.D.), there it seems that all
lines were drawn on the ground with sandal paste (candana-
kṣodārdra). The above circle having been thus drawn and coated
with sandal paste, another small concentric circle was drawn
with the radius of the gnomon. The gnomon was then placed
vertically with the periphery of its base in coincidence with
that circle. The gnomon was thus set up exactly in the middle of
the bigger circle. The verticality of the gnomon was tested by
means of four plumb lines hung on the four sides of the
gnomon
Gnomon Used for Finding the Directions
The rule in this connection has been described by
Brahmagupta in BrSpSi. III. 1. The same rule in other words
has been described by Bhāskara I in MBh. III. 2. In the Vāsanā
Bhāṣya, Pṛthūdaka Svāmī describes the details of determining
the directions. The level of the ground is ascertained by means
of water and a gnomon of 12 aṅgulas is set up. Find out two
points where the shadow of the gnomon enters into and passes
out of the circle. Bhāskara prescribes drawing out a fish figure
with these points. The thread line which goes through the
mouth and tail of the fish figure indicates the north and south
directions with respect to the gnomon. Brahmagupta says that
if the Sun is on the eastern side, then where the shadow-point
enters circle (in the forenoon) that point would be the west, and
the point where it emerges out (in the afternoon) is the east.
As the Sun moves along the ecliptic, its declination
changes. By the the time the shadow moves between the
forenoon and afternoon points as given above, the Sun , traverses
some distance of the ecliptic and, so, theoretically speaking, its