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The Astronomical Observatories of Jai Singh c15.s1.t6: Hindu Astronomical Instruments

The Astronomical Observatories of Jai Singh c15.s1.t6

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Hindu Astronomical Instruments

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73. The only instruments of practical utility for astronomical purposes described in ancient Hindu works are the sun-dial and clepsydra. An armillary sphere is also described as an instrument for purposes of demonstration. The only Hindu instrument of any antiquity actually found is the clepsydra, consisting of a metal bowl floating in a vessel of water.⁵

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⁵ It is the only instrument described in the *Ain-i-Akbari* (Ed. Jarret III, 16).

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The following is a summary of those parts of the early Hindu texts that deal with astronomical instruments. (i) The Clepsydra or Water clock is referred to in the *Jyotisha Vedānga*, where the amount of water that measures a *nāḍikā* (=24 minutes) is given. The more ancient form of water clock appears to have been simply a vessel with a small orifice at the bottom, through which the water flowed in a *nāḍikā*,⁶ but later on there came into use the form described in the *Sūrya Siddhānta* (XIII, 23): "A copper vessel, with a hole in the bottom, set in a vessel of pure water, sinks sixty times in a day and night, and is an accurate hemispherical instrument." The Pañcha siddhāntikā description ¹ (XIV, 32) is similar, but adds "Or else a nāḍikā may be measured by the time in which sixty slokas, each consisting of sixty long syllables, can be read out."

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⁶ J. F. Fleet, *The Ancient Indian Water Clock*, J.R.A.S., 1915, pp. 213-230.

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¹ Lala Chhotte Lāl's Jyotiṣa Vedāṅga, p. 12.

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A later description of the clepsydra is as follows: "A copper vessel, weighing 10 palas, six aṅgulas in height and twice as much in breadth at the mouth—this vessel of the capacity of 60 palas of water, and hemispherical in form, is called a ghaṭi. The aforesaid copper vessel, bored with a needle made of 3½ māshas ² of gold and 4 aṅgulas long, gets filled in one nāḍikā."

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² About 56 grains troy. Fleet quotes another rule, which gives the weight as a suvarṇa (= 16 māshas), and length 4 aṅgulas, drawn out round or square. Bhāskara simply says (XI, 8) it "should have a hole bored in its bottom."

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In practice, no doubt, the dimensions of the bowl and the orifice were determined by experiment. Bhāskara (XI, 8) indeed says: "See how often it is filled and falls to the bottom of the pail of water in which it is placed. Divide 60 ghaṭis of day and night by the quotient, and it will give the measure of the clepsydra."

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(ii) The Gnomon.—The sun-dial described in the early treatises is of the simplest kind, consisting of a vertical rod, or gnomon, divided into 12 divisions. The descriptions are of a theoretical nature, and do not apply so much to the construction of instruments as to theoretical calculations. The Pañchasiddhāntikā (XIV, 14-16) instructions are: "Mark from the centre three times the end of the gnomon's shadow, and then describe two fish figures. Thereupon describe a circle, taking for radius a string that is fastened to the point in which the two strings issuing from the heads of the fish figures intersect, and that is so long as to reach the three points marked. On the given day the shadow of the gnomon moves in that circle, and the base of the gnomon is the south-north line; and the interval, in the north direction, is the midday shadow." (III, 1-7) This means, mark on any particular day the extremity of the shadow at three different times—and these three points are supposed to lie on a circle, the centre of which is found (in the usual way) by the so-called fish figures.³

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³ The 'fish figure' is the common part of two intersecting circles.

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The Sūrya Siddhānta directions (III, 1-7) are more elaborate but relate to exactly the same type of dial. They are as follows:—

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"(1) On a stony surface, made water level, or upon hard plaster, made level, there draw an even circle of a radius equal to any required number of digits of the gnomon. (2) At its centre set up the gnomon of twelve digits of the measure fixed upon; and, where the extremity of its shadow touches the circle in the former and after parts of the day, (3) fixing two points upon the circle, and calling them the forenoon and afternoon points, draw midway between them, by means of a fish figure, a north and south line. (4) Midway between the north and south directions draw, by a fish figure, an east and west line: and, in like manner, also by the fish figures, between the four cardinal directions, draw the intermediate directions. (5) Draw a circumscribing square, by meansof the lines going out from the centre: by the digits of its base lines projected upon that, is any given shadow reckoned. (6) The east and west line is called the prime vertical (*sama-maṇḍala*): it is likewise denominated the east and west hour circle (*unmaṇḍala*), and the equinoctial circle (*viṣuvan maṇḍala*). (7) Draw likewise an east and west line through the equinoctial shadow (*viṣuvad-bhā*); the interval between any given shadow and the line of the equinoctial shadow is denominated the measures of the amplitude¹ (*agrā*).”

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¹ Distance of the sun at rising or setting from east or west point of the horizon.

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(iii) Armillary Sphere.—The Sūrya Siddhānta (XIII, 1-6) gives instructions for the making of an elaborate armillary sphere:—

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(2) “Let the teacher, for the instruction of the pupil ……(3) prepare the wonder working fabric of the terrestrial and stellar sphere (*bhūbha gola*). Having fashioned an earth-globe of wood, of the desired size, (4) fix a staff, passing through the midst of it and protruding at either side for Meru; and likewise a couple of sustaining bands and the equinoctial circle; (5) these are to be made with graduated divisions (*aṅgula*) of degrees of the circle (*bhagaṇa*). Further, by means of the several day-radii, as adapted to the scale established for those other circles, (6) and, by means of the degrees of declination and latitude marked off upon the latter, at their own respective distances in declination, according to the declination of Aries, etc., (7) three bands are to be prepared and fastened: these answer also inversely for Cancer, etc. In the same manner, three for Libra, etc., answering also inversely for Capricorn, etc.: (8) and, situated in the southern hemisphere, are to be made and fastened to the two band-supporters. Those, likewise, of the asterisms situated in the southern and northern hemispheres, of Abhijit, (9) of the Seven Sages (*Saptarṣayas*) of Agastya, of Brahma, etc., are to be fixed. Just in the midst of all the equinoctial band is fixed. (10) Above the points of intersection of that and the supporting bands are the two solstices (*ayana*) and the two equinoxes (*viṣuvat*). From the place of the equinox, with the exact number of degrees, as proportioned to the whole circle, (11) fix by oblique chords, the spaces (*kṣetra*) of Aries and the rest; and so, likewise, another band, running obliquely from solstice to solstice, (12) and called the circle of declination (*krānti*): upon that the sun constantly revolves giving light: the moon and the other planets, also by their own nodes, which are situated in the ecliptic (*apa maṇḍala*), (13) being drawn away from it, are beheld at the limit of their removal in latitude (*vikṣepa*) from the corresponding point of declination. The orient ecliptic point (*lagna*) is that of the orient horizon; the occident point (*astamgachhat*) is similarly determined. (14) The meridian ecliptic point (*madhyama*) is as calculated by the equivalents in right ascension (*laṅkodayās*), for mid heaven (*hamadhya*) above. The sine which is between the meridian and the horizon (*kṣitija*) is styled the day measure (*antyā*), (15) and the sine of the sun’s ascensional distance (*charadala*) is to be recognised as the interval between the equator and the horizon. Having turned upward one’s own place, the circle of the horizon is midway of the sphere. (16) As covered with a casing (*vastra*) and as left uncovered, it is the sphere surrounded by Lokāloka. By the application of water is made ascertainment of the revolution of time. (17) One may construct a sphere instrument combined with quicksilver; this is a mystery, if plainly described it would be generally intelligible to the world. (18) Therefore let the supreme sphere be constructed according to the instruction of the preceptor. In each successive age, this construction, having become lost, (19) is by the sun's favour again revealed to some one or other at his pleasure."

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(iv) Other Instruments—" So also," the text continues, "one should construct instruments (yantras) for the ascertainment of time. (20) When quite alone, one should apply quicksilver to the wonder causing instrument.¹ By the gnomon (sanku), staff (yashti) arc (dhanus), circle (chakra), instruments for taking the shadow of various kinds .......... (21), By water instruments, the hemisphere (kapāla), etc., by the peacock, man, monkey, and by stringed sand receptacles, one may determine time accurately. (22) Quicksilver-holes, water, and cords, ropes and oil and water, mercury, and sand are used in these: these applications, too, are difficult ..........

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¹ See the Siddhānta Siromani xi 50-51. The instrument appears to be a perpetual motion machine, which consists of a wheel with hollow (tangential) spokes which are filled with mercury. "The wheel thus filled will, when placed on an axis supported by two posts, revolve of itself." This is an old friend.

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(24) So also a dial (narayantra) is good in daytime, and when the sun is clear."

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Such is the orthodox Hindu text relating to instruments. Nothing of material value appears to have been added to these instructions until the methods of the Yavanas were introduced, by Mahendra Sūri and others; but Bhāskara (Siddhānta Siromani XI, 16) claims to have invented an instrument called Phalaka Yantra,² which, he says, is an "excellent instrument, calculated to remove always the darkness of ignorance and is the delight of clever astronomers." This instrument is simply a board divided by horizontals into 90 equal parts. At the centre of the 30th graduation from the top a pin, or style, is placed perpendicular to the board, and round it a circle is drawn of radius=30 divisions, which is graduated in ghaṭis and degrees, and attached to the pin is an index arm (paṭṭika). The instrument is suspended by a chain, and is used for observational purposes. It is in fact part of a very simple astrolabe. Bhāskara did not seem very pleased with his instrument, for, he concludes (XI, 40) by saying "But what does a man of genius want with instruments, about which numerous works have treated? Let him only take a staff in his hand, and look at any object along it, casting his eye from its end to the top. There is nothing of which he will not then tell: its altitude, dimensions, etc." This sums up, very well indeed, the attitude of Hindu astronomers.

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² Compare the 'Balance Khorarie ou Fézaire' described by Delambre Astronomie du Moyen Age, p. 521

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