There is a fascinating history regarding the construction of this observatory. Sawai Jai Singh II sent his men to various parts of the world. The men came back with manuals, astronomical tables and data on the advances made in the field of astronomy. La Hire's "Tables" was one of these manuals. Sawai Jai Singh II ordered the observatory to be constructed according to the data available in this manual. Amazingly, after Jantar Mantar was built, it was discovered that the observatory was more accurate than the Table itself.
Sawai Jai Singh had the choice either to construct the observatory with metal instruments or masonry instruments. The metal instruments, constructed according to the text of the Islamic school of astronomy, did not measure up to Jai Singh's expectations. So, he discarded them in favor of the instruments of stone and masonry that he himself designed. In this Observatory one can view the wonderful masonry instruments. The observatory has the Jaiprakash
Yantra, Samrat Yantra, Ram Yantra and the Composite instrument, which comprises of a sundial and a massive hemisphere. Jantar Mantar was built not only to verify astronomical observations made at
Jaipur, but also to stimulate interest in astronomy, which had become enmeshed in theory, superstition and religious jargon.