Rama Yantra
Jantar Mantar “Magic Sign”
Site The Delhi Observatory, known as the ‘Jantar Mantar’, was built on a broad, treeless plain some distance from the city walls. Only when the English founded a new royal seat for the viceroy, designed by Sir Edward Lutyens, did the observatory come to be absorbed into New Delhi’s massive housing development. A Great Samrat Yantra, two Jai Prakash Yantras and a Mishra Yantra have survived. But it emerges from William Hunter (‘Some accounts of the Astronomical Labours of Jayasinha’; Asiatic Researches, vol. 5, 1799) that there was originally also a Dakshino Bhitti Yantra used for observing celestial bodies in their meridian transit. (p67)
Architects Jai Singh
Jaganath
Materials Even today, the walls consist of the original quarrystone and mortar. This same limestone mortar was also used for smoothing down the rough masonry. Jai Singh himself gives ‘stone and limestone’ as the materials used in his observatory in Delhi. (p136, Construction Methods)
Staircases Average riser/tread average of Great Samrat Yantra: 28.2/34.0cm (p140)
Rama Yantra An instrument named after Maharaja Ram Singh. A drum shaped stone building which was used for establishing azimuth and zenith distances. Although these huge buildings have much the same function as those in Jaipur, they appear heavier, older and more monumental. (p77)
A mighty pillar, built of plaster covered stone towers up in the centre of each of the Rama Yantras in Delhi. This serves not only as the geometrical centre but also, thanks to its continuous cylindrical shape, as the visual point of repose in the endless circular movement of the sector-shaped graduated areas and the surrounding circular wall, which is broken up by keel arches. (p77-78)
In the Rama Yantras in Delhi, angles could be measured in the following way: the azimuth of the sun was obtained by halving the broad shadow which the stone pillar casts on the scales. The end of the shadow indicated its zenith distance. A piece of string could be attached to the centre of the circular surface forming the top of the stone pillar. It dangled over the edge of this circular surface and, for observing stars, as in Jaipur, it served as a sighting aid for the observer, who moved the other end of the string along the graduation marks of the sectors of the circle. If they wanted to measure the zenith distances of more than 45° then they had to take the string up along the vertical graduated areas of the circular wall. For this purpose, steps were provided at irregular intervals in the niches between the scales.
This meant that the height of the circular wall above the sectors of the circle (a) corresponds to the radius (b) minus half the diameter of the column in the centre (d). (p78)