India, Feb. 21 -- Delhi's Jantar Mantar, currently undergoing the first steps of a planned restoration, has four instruments that are a mix of science and mystery. Three of them were set up by the Rajput ruler Sawai Jai Singh who built five observatories in northern India 300 years ago. The fourth, which has become this Jantar Mantar's signature, is the Misra Yantra with its semicircular arcs. Believed to have been added later by one of Jai Singh's sons, it had multiple purposes, some of which are not yet fully understood....