A highly imaginative device, spherical walls cut by an inclined stairway pointing exactly to the North Star showed the local time.
Fascinated by science and astronomy, the maharaja of Jaipur Jai Sing II, a fine connoisseur of Astronomy, built this impressive observatory between 1728 and 1733. There are 17 open-air instruments that make up as many sculptures with very contemporary shapes. Each of them has a function, such as the Nari Valaya Yantra, with which one calculates the hours in different parts of the globe, or the Brihat Samrat Yantra, a huge sundial.
Instead of brass or metal instruments, Jai Singh opted for masonry instruments, giving priority to durability and precision over mobility. By making large,
immovable instruments, Jai Singh sacrificed facility for supposed accuracy. Another innovation and contribution of Jai Singh is that he himself devised the
Samrat Yantra, the Jai Prakash Yantra and the Ram Yantra. In addition to it, the astronomer king used other stone instruments, such as the mural quadrant and
cylindrical dial. The Samrat Yantra is, in principle, is very simple form of Sun-Dial, but it is an efficient instrument, and, as Jai Singh designed it, a
dignified structure.
The Jai Prakash is called by Jagannath Surya Yantra Shiromani the crest jewel of all instruments. It is a hemisphere, on the concave
side of which is mapped out certain co-ordinates. The Jai Prakash is found only at Delhi and Jaipur. The diameter of Jai Prakash at Jaipur is 17 feet 10 inches.
The Diganisa Yantra, a simple and useful instrument, is found in Jaipur, Ujjain and Varanasi observatories. This device is formed of a pillar surrounded by two
circular walls. The central pillar is generally about 4 feet high, and the inner wall the same height, while the outer wall is twice that height. Cross wires
are stretched from the cardinal points on the outer wall, and both walls are graduated. The instrument may be described as a fixed large circular protractor.
The Narivalaya Yantra (Circular Dial) is mentioned by Jagannath and it occurs at Jaipur, Ujjain and Varanasi. It may be described as a cylindrical dial—the axis
of the cylinder pointing north and south, and the northern and southern faces being parallel to the plane of the equator. The Dakshinovritti Yantra, a Meridian
Circle, is a useful and popular -among-other- observatories instrument. This mural quadrant sort of device was found in most mediaeval observatories. It consists,
essentially, of a wall in the meridian, and on the wall is two graduated quadrants and centre pins, which were used for observing the altitudes of heavenly bodies
when passing the meridian. Originally there was one at each observatory, but that at Delhi has been destroyed.