The Jantar Mantar, in Jaipur, is an astronomical observation site built in the early 18th century. It includes a set of some 20 main fixed instruments. They are monumental examples in masonry of known instruments but which in many cases have specific characteristics of their own. Designed for the observation of astronomical positions with the naked eye, they embody several architectural and instrumental innovations. [Source: Vistara, catalogue of the exhibition]
The Jai Prakash may well be Jai Singh’s most elaborate and complex instrument. It is based on concepts dating to as early as 300 B.C. when the Greco-Babylonian astronomer Berosus is said to have made a hemispherical sundial. Hemispherical dials also appear in European Church architecture during the Middle Ages, and at the observatory in Nanking, China in the late 13th-century. The Jai Prakash, however, is much more elaborate, complex, and versatile than any of its predecessors.