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

SETTING UP OF THE GNOMON 335
Bhāskara I in his commentary on the Āryabhaṭīya tells us
that there was a difference of opinion amongst astronomers in
his time regarding the shape and size of gnomon (also called style).
Some astronomers prescribed a gnomon with its one-third in the
bottom of the shape of a prism on a square base (caturasra), one-
third in the middle of the shape of a cow's tail (go-pucchākāra).
and one-third at the top of the shape of a spear-head (Śūlākāra)
and some others prescribed a square prismoidal (samacaturasra).
gnomon. The followers of Āryabhaṭa I, he informs us, prescrib-
ed the use of a broad (pṛthu), massive (guru), and large (dīrgha
cylindrical gnomon, made of excellent timber and free from any
hole, a scar or knot on its body. In the above stanza, Bhāskara I
prescribes this last kind of gnomon : the other two kinds he
proves in the commentary to be defective and so he rejects them.
For getting the shadow'end easily and correctly the cylindri-
cal gnomon was surmounted by a fine cylindrical iron or wooden
nail fixed vertically at the centre of the upper end. The nail
was taken to be longer than the radius of the gnomon, so that
its shadow was always seen on the ground.
Certain writers, Bhāskara I tells us in the commentary,
prescribed a gnomon of half a cubit (=12 aṅgulas) in length
and having twelve divisions. But according to Bhāskara I
(although it was the usual custom) there was no such hard and
fast rule. The gnomon could be of any length and any number
of divisions. The gnomon should, however, be large enough, so
that the rings of graduation on the gnomon may be clearly seen
on the shadow. A broad and massive gnomon was preferred
because it was unaffected by the wind.
Brahmagupta describes gnomon which at the bottom is
two aṅgulas wide, pointed as a needle., 12 aṅgulas in length, and
full of holes from the basic circular part to the pointed
extremity. (BrSpSi. XXII. 39).
As regards testing the level of the ground, Bhāskara I
observes :
When there is no wind, place a jar (full) of water
upon a tripod on the ground which has been made
plane by means of eye or thread, and bore a (fine)
hole (at the bottom of the jar) so that the water may