The Astronomical Observatories of Jai Singh c9: Chapter VI.—Masonry Instruments

The Astronomical Observatories of Jai Singh c9

Language: English

c9.s1 Samrāṭ Yantra — 39 parts

Chapter VI.—Masonry Instruments

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27. The masonry instruments, which vary in size from a few feet to 90 feet in height, are Jai Singh’s chief work. It has already been related how Jai Singh discarded brass instruments, and built massive masonry ones in their place. His reasons appeared to be, but were not altogether, sound. The brass instruments were, he said, faulty, because of their mobility and size.¹ The axes became worn and the instruments untrue; the graduations were too small for fine measurements, etc. His remedy was to make large, immovable instruments: but he thus stereotyped his designs, and hindered further improvements. The larger and more immobile an instrument is the greater is the difficulty in making alterations and improvements. Jai Singh sacrificed facility for supposed accuracy.

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¹ The contrast with the procedure in Europe is interesting. The European scientist recognised the inevitability of error, and took measures to counteract it (e.g., with the micrometer, vernier, telescopic sights, etc., etc.) Even a modern theodolite, as a useful astronomical instrument, is worth more than all Jai Singh’s large buildings. Possibly, Jai Singh’s power and wealth inclined him to move in a direction that could not lead to the desired end. See page 90.

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Hunter states that Jai Singh himself devised the Samrāṭ Yantra, the Jai Prakāś, and the Rām Yantra. These three instruments are indeed peculiar to Jai Singh’s observatories, and must be to some extent attributed to Jai Singh’s personal ingenuity.² Jai Singh used other stone instruments, such as the mural quadrant and cylindrical dial; but these were not mentioned specially in the preface, because they were common to many observatories. They are, however, mentioned in Jagannāth’s introduction to the Samrāṭ Siddhānta (see page 3).

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² See page 86.

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The masonry instruments are:—
(a) Samrāṭ Yantra at Delhi, Jaipur (2), Ujjain, and Benares (2). Figures 34, 35, 43-46, 66 and Plate XV.
(b) Jai Prakāś at Delhi and Jaipur. Figures 30, 32, 33 and Plate XVIII.
(c) Rām Yantra at Delhi and Jaipur. Figures 47, 48, 49, 59 and Plate XVII.
(d) Digaṁśa Yantra at Jaipur, Ujjain and Benares. Figures 63, 65 and Plates XXIV and XXVI.
(e) Dakṣiṇovṛtti Yantra at Jaipur, Ujjain and Benares. Figures 56 and 62.
(f) Nari-valaya Yantra at Jaipur, Ujjain and Benares. Figures 53 and 65.
(g) Vṛtti Śhaṣṭāṁśaka at Delhi and Jaipur.
(h) Miśra Yantra at Delhi. Figures 50, 51 and Plate XIX.
(i) Rāśi Valaya at Jaipur. Figures 54 and 55.
(j) Kapāla at Jaipur. Figure 31.

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The last three of these instruments are possibly of later date than Jai Singh. They are mentioned in neither of the contemporary lists.

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28. The Samrāṭ Yantra or ‘Supreme instrument’¹ is, as its name implies, the most important. It is an equinoctial dial, consisting of a triangular gnomon with the hypotenuse parallel to the earth’s axis, and on either side of the gnomon is a quadrant of a circle parallel to the plane of the equator. It is, in principle, one of the simplest ‘equal hour’ sundials.

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In figures 34 and 35, AB is one edge of the gnomon, the angle ABC is equal to the latitude of the place, EF and GH are at right angles to AB, as also are DF, MH. If KL is the direction of the sun, then the arc KG indicates the time before noon, and the angle HGL the declination, or sun’s angular distance from the equator. In the actual structure, the considerable width of AA¹ and GE (each being over 9 feet at Jaipur) practically duplicates the instruments. Each edge of the quadrants is graduated in hours and minutes,² as well as in degrees, and each edge of the gnomon has two scales of tangents, one from H to B, and the other from F to A. In the figure tan HGL = HL/GH, and GH is the radius of the quadrant MKG.

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¹ Williams says the Arabic name was ‘Kootoop bede in Hindu droop.’

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² They were originally graduated in *ghatis* and *palas*.

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The shape of the gnomon is generally a parallel trapezium, as in figure 34, ABB'C. In the same figure GE represents the position of the quadrants as they enter the gnomon, HG = FE is the radius, and the lines radiating from E and G show the construction of the scales of tangents on the edge AB.

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In the following list the examples of the Samrāṭ Yantra are enumerated and their dimensions (with reference to figure 34) are given:—

Samrāṭ Yantra

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| | Height. | Base BC. | Hypotenuse AB | Radius GH=EF | Width of Quadrant GE | Angle ABC approximate. |
| | AC | AC | | | | |
| Delhi . . . | 68' 0" | 60' 4" | 113' 6" | 128' 6" | 49' 6" | 7' 7¼" | 28° 37' |
| Jaipur . . . | 89' 9" | 75' 3" | 146' 11" | 174' 0" | 49' 10" | 9' 3¼" | 26° 53' |
| | | 18' 6" | 37' 0" | 40' 8" | 9' 1¼" | | |
| Ujjain . . . | 22' 0" | 18' 6" | 43' 6" | 47' 6" | 9' 1" | | 23° 10' |
| Benares . . . | 22' 3½ | 16' 11½ | 35' 10" | 39' 8¼" | 9' 1¼" | 5' 10" | 25° 14' |
| | 8' 3" | 4' 9" | 10' 0½" | 11' 1¼" | 3' 2" | 1' 9" | 25° 19' |

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These dials give apparent solar time, which varies from day to day, owing to (1) the eccentricity of the earth’s orbit and its consequent more rapid angular motion in the winter (when it is nearer the sun) and its slower motion in summer; (2) the obliquity of the ecliptic.³ Consequently a clock going regularly does not agree for long with solar time. In India there is another element of difference to consider, due to the standard time being fixed for the longitude of 82½° degree east of Greenwich, or 5½ hours before Greenwich time. A table that will enable the observer to compare roughly the dial time with clock time is given in appendix C.

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³ These are the two principal causes, but all other causes combined only alter the equation of time by a few seconds.

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Fig 31. KAPALA, JAIPUR.

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Fig 33. JAI PRAKAS, DELHI.

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Fig 30. JAI PRAKAS, JAIPUR.

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Fig 32. JAI PRAKAS, DELHI.

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29. The Jai Prakāś is called by Jagannāth sarva yantra śiromaṇi ‘the crest jewel of all instruments.’ It is a hemisphere, on the concave side of which are mapped out certain co-ordinates. Cross wires are stretched north to south and east to west, and the shadow of the intersection of the wires, falling on the surface of the hemisphere, indicates the position of the sun in the heavens other heavenly bodies can be observed direct by ‘placing the eye’ at the proper graduated point, and observing the passage of the body across the point of intersection of the wires. For this purpose passages are cut into the hemisphere, and the instrument is duplicated.

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The construction of the instrument is seen in the plan and section shown in plate XVIII, and in figures 30, 32 and 33. Figure 38 shows a projection of a complete Jai Prakāś. The outer circle represents the horizon and is graduated in degrees. From the centre azimuth lines and altitude circles are drawn. (These are not all shown in the plate.) 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 (in the plate 28°37′ approximately). The equator, AEC, and tropics, fff (Capricorn), ggg (Cancer), and intermediate diurnal circles (not shown) are drawn. The equator cuts the meridian at a point, E, at a distance from the centre point equal to the latitude of the place (28°37′), and the other circles cut the meridian at distances 23½°, 20°12′ and 11°30′ on either side of the equator. Through the pole, hour circles Pa¹ Pa², Pa³, etc., are drawn. The circles hh₁, ii₁, jj₁, kk are circles of the signs, and are such, that, when the shadow falls on any one of them, the corresponding sign is on the meridian. Two such circles cut each of the seven diurnal circles on the meridian, and cut the neighbouring diurnal circles at the proper intervals. At Jaipur a similar instrument (figure 31) called Kapāla (‘cup’ or ‘hemisphere’) is so constructed, as to show ‘rising signs.’ In this instrument the edge of the hemisphere corresponds, not to the horizon, but to the solstitial colure (i.e., the circle passing through the poles and the solstitial points), and, thus, is the Jai Prakāś turned through a right angle.²

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¹ The method is very crude, and the observations must have been very rough approximations only.

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² The Jai Prakāś was known to the Arabs as al-Maṣṭarah. For descriptions see L.A. Sédillot's Mémoire, and Blagrave's Art of Dyalling, quoted below (p. 86).

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The Jai Prakāś is found only at Delhi and Jaipur. The diameter of that at Delhi is 27 feet 5 inches and that at Jaipur 17 feet 10 inches. (See plates XVIII and XXI.)

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30. The Rām Yantra is the third of the stone instruments mentioned in the preface to the Zij Muḥammad Shāhī (page 13). The Paṇḍits say it was named after Rām Singh, a predecessor of Jai Singh’s. According to Hunter the instrument was also known as Ustuwani, which was the name given by al-Bīrūnī³ to an astrolabe on a cylindrical (orthographic) projection he devised. The Rām Yantra is a cylindrical instrument open at the top and having at its centre a pillar. The floor and the inside of the circular wall are graduated in scales of tangents for altitude and azimuth observations. The height of the wall from the graduated floor is equal to the distance from the circumference of the central pillar to the inside of the wall. To facilitate observation the floor is broken up into sectors (see figure 47 and plate XVII), and, consequently, as in the case of the Jai Prakāś, complementary buildings had to be constructed (see figure 41). The walls also are broken up, and one section of the wall corresponds to one sector. At Delhi there are 30 sectors, each of 6 degrees, in each building, but at Jaipur there are 12 sectors only, and their angle is 12 degrees in one instrument and 18 degrees in the other, the spaces between them being respectively 18 and 12 degrees.

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³ The Chronology of Nations, p. 357f.

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On each side of the wall sections are notches in which sighting bars can be placed horizontally. The construction is illustrated in plates XIII, XVII, and XXI and in figures 47, 48 and 49. Figure 41 gives a good view of the buildings as a whole. Examples of the Rām Yantra exist at Delhi and Jaipur only and the Jaipur instrument is quite a modern one.¹

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¹ It was built in 1891. There are also two small Rām Yantras, which were constructed as models.

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The dimensions of the two instruments are :

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| | Inside diameter. | Height. | Diameter of pillar. |
| Delhi . . . . . . . . . . | 54' 7½" | 24' 8" | 5' 3½" |
| Jaipur . . . . . . . . . . | 23' 1" | 11' 4" | 2" |

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31. The Digamśa Yantra (‘Azimuth instrument’), although not actually mentioned by Jai Singh in the preface, is given, however, in Jagannāth’s list (see p. 3). It is a simple and useful instrument, and examples of it still exist at Jaipur, Ujjain and Benares. The instrument consists of a pillar surrounded by two circular walls (see plates XXI and XXVI, DD). The central pillar is generally about 4 feet high, and the inner wall the same height, while the outer wall is twice that height.

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Cross wires are stretched from the cardinal points on the outer wall, and both walls are graduated. The inner wall is a convenient height for a man to walk on and to look over the outer wall. By the aid of a movable string and an assistant, azimuth (horizontal angles) observations can be made with fair accuracy. The instrument may be described as a fixed large circular protractor.

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The dimensions of the several Digamśa Yantras are :

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| | DIAMETERS. | | HEIGHTS. | |
| | Outer wall. | Inner wall. | Outer wall. | Inner wall. |
| Jaipur . . . . . . . . . . | 27' 0" | 17' 6" | 6' 5" | 3' 2½" |
| Ujjain . . . . . . . . . . | 36' 10" | 24' 4" | 8' 10" | 4' 6" |
| Benares . . . . . . . . . | 31' 6" | 21' 0" | 8' 4" | 4' 1" |

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FIG. 34. DIAGRAM OF SAMRAT YANTRA.

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FIG. 35. DIAGRAM OF SAMRAT YANTRA.

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FIG. 36. CONSTRUCTION FOR THE NIYAT CHAKRA.

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FIG. 37. DECLINATION GRAPH.

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FIG. 38. DIAGRAM FOR THE JAI PRAKAS.

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Jagannāth’s description of the Digamśa Yantra is as follows :—“Make a circle on the ground with any radius. This circle is called the horizon. We shall have to make three horizons here. On the first circle build a solid pillar. On the second circle build a ring-like wall as high as the pillar on the first circle. On the third circle make a ring-like wall twice as high as either of the former. On all these horizons mark the east to west and north to south lines and degrees and minutes. Stretch tightly two threads across the exterior wall, to represent the east and west and north and south lines, intersecting at right angles over the centre of the horizons. At the centre of the pillar fix securely one end of a string, and to the other end of the string fasten a stone and place it over the edge of the third horizon. This thread is called the ‘thread of the circle of vision.’”

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32. The Narivalaya Yantra (‘Circular dial’) is mentioned by Jagannāth and it occurs at Jaipur, Ujjain and Benares. It may be described as a cylindrical dial—the axis of the cylinder pointing north and south, and the northern and southern faces being parallel to the plane of the equator. At the centre of each face, and at right angles to it, is an iron style surrounded by circles graduated into hours and minutes and ghaṭis and palas respectively. The shadow of the style marks the time of the day, and the instrument also shows, very effectively, the passage of the sun across the equator (the equinoxes). See figures 53 and 65. Jagannāth remarks, about this instrument, that it is not of much value, because it only gives readings for northerly observations. This applies to some extent to the Benares instrument (see figure 65), but not to those at Ujjain and Jaipur.

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33. The Dakshinovritti Yantra (‘Meridian circle’) is like the mural quadrants found in most mediaeval observatories. It consists, essentially, of a wall in the meridian, and on the wall are two graduated quadrants and centre pins (see figures 56 and 62 and plates XXIV and XXVI), which were used for observing the altitudes of heavenly bodies when passing the meridian. The instrument corresponds to the modern transit circle. Originally there was one at each observatory, but that at Delhi has been destroyed.

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33(a). The Shasthāmśa Yantra (‘Sextant’) occurs at Delhi and Jaipur only and is really another form of meridian circle. It is a large graduated arc lying in the meridian and is built in a ‘dark room’ at the bottom of the masonry work that supports the huge quadrants of the Samrāṭ Yantra. A small orifice some 30 or 40 feet above admits the light of the sun at noon and the image of the sun on the graduated arc marks with fair accuracy the sun’s altitude. It is thus the aperture dial of the Muslims (see p. 82). At Jaipur there are two ‘dark rooms,’ one under each quadrant of the Samrāṭ and in each room are two arcs the radius of each being 28 feet 4 inches. The ‘dark room’ at Delhi is at present inaccessible.

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34. Of other masonry instruments there are the Miśra Yantra (‘mixed instrument’) at Delhi and the Rāśi Valaya (zodiac dials) at Jaipur. There are some indications that these two instruments, or rather sets of instruments, were not devised by Jai Singh, and, therefore, they will be described in detail when the observatories at Delhi and Jaipur are dealt with. The most notable feature of the Miśra Yantra is the set of arcs for meridians at Greenwich and Zurich on the west, and two corresponding places on the east. The Rāśi Valaya is a set of twelve dials connected with the rising signs, and which show the sun's latitude and longitude.

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35. Of these instruments it is claimed that Jai Singh devised the Samrāṭ Yantra, Jai Prakāś and Rām Yantra. The evolution of these instruments will be dealt with in a concluding chapter, but it may be remarked here that Jai Singh's ingenuity was chiefly concerned with the transference of designs, previously executed in instruments of comparatively small size, to huge masonry instruments. No new invention, in the ordinary sense of the word, was attempted. The Samrāṭ Yantra is, in principle, a very simple form of sun-dial, but it is an efficient instrument, and, as Jai Singh designed it, a dignified structure. There is, so far, no evidence to show that the tangent scales on the edge of the gnomon had been previously used as on the Samrāṭ Yantra; therefore, besides the general design, we may credit Jai Singh with this device. The Jai Prakāś or ‘invention of Jai,’ as it may be called, and which Jagannāth calls the ‘crest jewel,’ is really a sort of combined armillary sphere. Possibly the astrolabe projections suggested the idea to Jai Singh. In a manuscript copy of a work by Abdul Ali Barjendi¹ (died A.D. 1523) most of the details of such an instrument as the Jai Prakāś are given. Jai Singh's duplicated instrument is, however, his own design, and, probably, the introduction of the culminating sign lines must be attributed entirely to his own invention.

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¹ Abdul ‘Ali b. M. al-Ḥusain, Niẓām al-Dīn al-Barjendi wrote a commentary on Naṣīr al-Dīn's recension of the Almagest, a commentary on Naṣīr al-Dīn's treatise on the astrolabe, a comment on Ulugh Beg's tables, a treatise on astronomy, etc. I am indebted to Khān Bahādur Pīr Muẓaffar Aḥmed of Delhi for the loan of this manuscript, which was written out by one Quṭb b. ‘Abdul Jalīl in A. H. 1066 (=A.D. 1655) at Ḥyderābād. Its date and its presence at Delhi suggests the possibility of its having once belonged to Jai Singh's library.

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The Rām Yantra is only original with respect to its size and the duplication of the instrument. The meridian lines of other places on the Miśra Yantra at Delhi was not a new idea. It had, at any rate, been worked out for vertical gnomons. The Rāśi Valaya seems to be entirely original, but it is of doubtful utility as an instrument for observation.

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Samrāṭsiddhānta — Jagannātha Samrāj 1707, Sanskrit

The Astronomical Observatories of Jai Singh c9: Chapter VI.—Masonry Instruments

Contents

Chapter VI.—Masonry Instruments

Samrāṭ Yantra

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