The Astronomical Observatories of Jai Singh c13.27

c13.27

The Chakra Yantra is shown in the plan at CC. It is an equatorial, and was common to most mediaeval observatories. It consists of an iron circle (declination circle) 3 feet 7 inches in diameter, one inch thick and two broad, faced with brass, on which degrees and minutes are marked. The circle is fixed so that it can revolve round an axis parallel to the earth's axis. At the southern extremity of this axis, and on the pillar which supports the instrument, is a graduated circle (hour circle) in the plane of the equator (figure 65). There is no pointer for this hour circle, and according to Hunter there was none in 1797. Attached to the centre of the declination circle is a sighter, consisting of a hollow brass tube (figure 68), but this is comparatively new. Hunter wrote: "Observations with this instrument cannot have admitted of much accuracy, as the index is not furnished with sights; and the pin by which it is fixed to the centre of the circle is so prominent, that the eye cannot look along the index itself." In figure 68 can be seen what is probably the old index and also the new tube sighter.