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