Eternal India Encyclopedia

Eternal India

encyclopedia

Ancient Concepts, Sciences & Systems

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

facilitate

observations.

Wall sections are provided

with

notches

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

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.

(J.C.B.) & (G.S.D.B.)

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.

Schematic diagram for the markings on the Jai

Prakash

The Jai Prakash : This

instrument consists of two

complementary

concave

hemispheres,

situated

im-

mediately

south

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.