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