YANTRA, Yantri, or Jantri, a Hindu almanac, dial, altitude and azimuth instruments.
Raj Yantra is used for ascertainiug the alti ide of the heavenly bodies and the longitude of laces, referred to Lucknow (secular capital) and Ajodliya (religious capital) as circles of first teridian. If the longitude of places, having ucknow as a first meridian, are to be ascertained, len the circle marked 26° 51', being the altitude Lucknow, must be uppermost, and so for jodhya.
Dltruba Yantra is used to find the direction of le poles. The instrument consists of a pointer, hose length is equal to the radius of the circle trough whose centre it passes at ri,ght angles. he circle is divided into 60 equal parts. It is so aced at noon that the shadow of the pointer ay fall at the 45th part.
Pratod Yantra is used to measure time. This an hour rod, whose horizontal section is a zular octagon, and the breadth of whose base to the breadth of its top as 3 to 2. The rod is )out 27 inches long, having near the top a 'oove on each of its sides to receive a stick tached to it, which is about 9 inches long. The ngth of the day varies from 26 to 33 dunda. he instrument is used thus: The length of the ay being known, the little stick is made to pass trough the groove marked with tho length in ma. The rod is then made to stand perpen Lcular to the horizon, facing the sun, so that the tadow may fall on the side which marks the ngth of the day. Before noon the shadows show te hours past, and after noon the hours reamin g to sunset.
Khapru Kidhup-ghari, a universal sun he wire from south to north, representing the cis of the earth, is in the place of the gnomon of to common sun-dial ; and the shadow cast by tis wire on the concave semi-cylindrical surface, .ves the time of day to within 5 minutes for a zy of 12 hours. The graduated arc to the north the brass meridian upon which the dial is clo tted according to the latitude of the place. The tadow cast from the transverse wire in the plane the equator tells the declination of the sun, id hence the month of the year. The vertical ip of brass to the south will give the time of day lin a high latitude, where the sun rises at three and sets at nine. The dial is graduated for 12 hours, acconling to the European system, and likewise for 30 ghurees (equal to 12 hours),accord ing to the Ilindu system. The instrument is levelled by turning the foot screws until the threads of the two plummets respectively touch the edge of lines which are marked in the adjacent bars. This sun-dial is known as the Khapru kidltup-ghari, or tile sun time, from its resem blance to the shape of a tile.
Moan Vaidra.—Equatorial altitude and azimuth instrument, used by ilindu astronomers. The mode of using it is described in Herschel's Astronomy, para. 182.—Gorernment of Oudh.