Eternal India Encyclopedia

Eternal India encyclopedia

Ancient Concepts, Sciences & Systems

The Jai Prakash : This instrument consists of two complementary concave hemispheres, situated im- mediately south of the Samrat Yantra. It is also called the ’crest jewel of all instruments'. The surface of each hemisphere is marked with several lines for meas- uring the altitude, azimuth, declination, hour angle, etc. of any object in the sky.

Delhi meridian at angles of 77°16' W, 68°34W, 68°01'E and 75° 54' E. The planes of these semicircles may be said to correspond to meridians at places whose longitudes differ from that of Delhi by these angles. They seem to be matching respectively with Greenwich Observatory, Zurich Observatory a village in Japan and a town on Pic Island in Lake Superior, Canada. However It is obvious that these are coincidences rather than premeditated thoughts considering the fact that the Zurich Observatory came into existence some sixteen years after Jai Singh's death! Of these instruments, it is claimed that Jai Singh devised the Samrat Yantra, the Jai Prakash and the Ram Yantra. He reasoned that the smaller brass instruments were faulty because their axes became worn and their graduations were too small for fine meas- urements. His remedy thus was to make large and immovable instruments. But by doing so he unfortunately sacrificed any facility for improvement, like adding a vernier scale, for example, for accu- racy. His object was the rectification of star catalogues, the calen- dar, prediction of eclipses and so on. His scheme of astronomical work was truly notable and his observatories form noble monu- ments of a remarkable personality. While Jai Singh's efforts were mainly in the northern part of India, there are records to show that for the first time on Indian soil a telescope was used to make stellar observations in Pondicherry, a coastal town in South India, thirty five years before Jai Singh founded his observatories. On December 19, 1689, Father Richaud, a member of the Society of Jesus focussed his small telescope towards the sky from Pondicherry and in course of time discovered a comet as well as the binary nature of the bright star Alpha Centauri. Later in 1786, a private observatory was set up in Madras by William Petrie, a small telescope being the main instrument. In 1790 the observatory was taken over by the East India Company with one Michael Topping as the Company astronomer. In 1792 the observatory building came up at Nungambakkam, Madras. It made important contributions for well over a century and paved the way for the establishment of the solar physics laboratory at Kodaikanal in 1900. SELECTED REFERENCES Scientists (Dhanvantri, Cavaka, Susruta, Varahamihira, Ar- yabhata, Bhaskaracharya) New Delhi 1990. D.M.Bose (Chief Ed) A Concise History of Science in India. New Delhi 1971. S.K. Biswas (Ed.) Cosmic Perspectives, Cambridge 1989. B.V. Subbarayappa and K.V. Sarma (Eds). Indian Astronomy. A Source Book. Bombay 1985. N. Kameswara Rao, V. Vagiswari and Christina Lousis, "Father J. Richaud and early telescope observations in India", Bulletin of the Astronomical Society of India (1984). Astronomy in Indus civilisation and during Vedic times by A.K. Beg and Post-Vedic Astronomy by S.D. Sharma in Indian Jour- nal of History of Science, Nos-1-4 Vol. 20. Jan-Dee 1985, Indian National Science Academy, New Delhi. (J.C.B.) & (G.S.D.B.)

Schematic diagram for the markings on the Jai Prakash

Crosswires are stretched from north to south and from east to west. The shadow of the intersection of these wires, falling on the .surface of the hemisphere, indicates the position of the Sun in the sky. Other celestial bodies can be observed directly by 'placing the eye' at the corresponding shadow cast by the object. That is, the ce- lestial object, the intersection of the- crosswires and the eye should be in one straight line. In this figure, the outer circle represents the horizon and is graduated in degrees. From the centre, which represents the zenith (denoted by Z), azimuth lines and altitude circles are drawn (not all are shown). The pole P is at a point on the meridian line BD, at a distance from the point B equal to the latitude of the place. It may be recalled here that the latitude of the place is equal to the altitude of the pole above the horizon of that place. The equator AEC and the tropics fff (Capricorn), ggg (Cancer) and intermediate circles are drawn at appropriate distances from the pole to facilitate the meas- urement of declinations. Through the pole, hour circles are drawn. The circles hh, ii, jj and kk are circles of the zodiacal signs, and are drawn such that when the shadow of the interesection of the crosswires cast by the Sun falls on any one of them, the corre- sponding sign is on the meridian. Only the Delhi and Jaipur observatories are fitted with a Jai Prakash dial. The diameter of the Delhi instrument is 27.5" and that at Jaipur is 17.10" The Ram Yantra is a cylindrical instrument

which is open at the top and has a central pillar. The in- side circular wall and the floor are graduated and the wall broken up into a se- lected number of sections to facilitate observations. Wall sections are provided with notches in which sighting bars can be fitted horizontally. This instru- ment also is in the Delhi

and Jaipur observatories only. The Misra Yantra : This is the mixed instrument and is so named because it combines four separate instruments in one struc- ture. Of these, the Niyat Chakra occupies the middle of the building and consists of a gnomon with two graduated semicircles on either side. These semicircles lie in planes inclined to the plane of the