Jyotihshastra: Astral and Mathematical Literature c4.s6.1

c4.s6.1

The earliest observational instrument in use in India was the śaṅku or gnomon, employed to find the cardinal directions in the Śulbasūtras. Since the fourth century B.C. both the śaṅku and the nāḍikā or outflowing water-clock have been used (with linear zig-zag functions) to determine time within the solar year and within any period of daylight. More elaborate uses of the śaṅku as an instrument for measuring local time and terrestrial latitude are given in every siddhānta and karaṇa in the chapter on tripraśna; eventually the noon equinoctial shadow cast by the śaṅku was used to characterize the latitude of localities mentioned in late medieval geographical lists.²⁷²