Jantar Mantar, which is actually pronounced, as ?Yantra Mantra?, yantra for instrument and mantra for formula. A huge sundial known as ?Samrat Yantra? or ?Prince of Dials?, meant to measure accurate time of the day within half a second and the declination of the sun and other heavenly bodies dominates it. Jai Singh himself designed this yantra. Other yantras were also meant for the study of heavenly bodies, plotting their course and predicting eclipses. The Jantar Mantars may have fallen into disuse but they remain an integral part of India?s scientific heritage. It presents that the spirit of scientific enquiry was not dead in India and would have yielded rich results if only an opportunity of research and development had been given to it.