The Astronomical Observatories of Jai Singh c10: Chapter VII.—The Delhi Observatory or Jantar Mantar

The Astronomical Observatories of Jai Singh c10

Language: English

Chapter VII.—The Delhi Observatory or Jantar Mantar

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For the Delhi observatory, known as the Jantar Mantar, we have the following approximately correct elements :— Latitude 28° 37' 35" N.¹ Longitude 77° 13' 5" E. of Greenwich. Height above the sea-level, 695 feet. Magnetic declination E. 1° 45', in 1915. Annual variation—1'. Local time 12 minutes 12 seconds after standard time.

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¹ In 1734 Father Boudier, who helped Jai Singh, obtained 28° 37' N. and 75° 0' East of Paris for the Delhi observatory. Rennel quotes Boudier as giving longitude 77° 40'. (The longitude of the Paris observatory is 2 30' 13·5" E. of Greenwich.) Hunter gives Lat. 28 37' 36" and Long. 77 2' 27" E. For the latitude Jai Singh obtained 28 39' 0". See page 129.

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36. The observatory is 3 miles 3½ furlongs almost due south from the Pir Ghāib, the Trigonometrical Survey point on the Ridge, near to Hindu Rao’s House. It is also 1 mile 7½ furlongs 32° west of south from the Jama Masjid. In the projected new city the observatory borders (on the east) the road leading from the railway station to the Secretariat and Government House. It consequently will be a notable feature in the Imperial Capital and, apart from its historical value, it is desirable that it be made, by suitable surroundings and proper restoration, as dignified as possible.

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The general plan² (plate XIII) of the observatory shows the following structures :—
(a) The Samrāṭ Yantra (‘Supreme instrument’), a huge equinoctial dial, Figures 40, 43-46 and plate XV.
(b) The Jai Prakāś, consisting of two hemispherical structures, just to the south of the Samrāṭ Yantra. Figures 41 and 42 and plate XVIII.
(c) The Rām Yantra, consisting of two circular buildings to the south of the Jai Prakāś. Figures 41, 47-49 and plate XVII.
(d) The Miśra Yantra (‘mixed instrument’), north-west of the Samrāṭ Yantra. Figures 50 and 51 and plate XIX.
(e) Two pillars south-west of the Miśra Yantra.
(f) A measuring platform, just south of the Miśra Yantra.

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² The Delhi plans were prepared for me by the Public Works Department, under the superintendence of Mr. Glen, Executive Engineer.

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37. The Samrāṭ Yantra is the central building of the observatory. It is the largest and most imposing, although a considerable portion of it is below the surface of the earth. It is, indeed, built into a quadrangular excavation some 15 feet deep, 125 feet from east to west, and 120 feet from north to south. The structure is 68 feet high, of which 60·3 feet is above the earth’s surface; 125 feet from east to west, and 113·5 feet from north to south. The details are exhibited in the plans and photographs (plate XV and figures 40, etc.). The essential parts are the inclined edges of the huge gnomon and the quadrants attached to it.³ The edges of the gnomon point to the celestial north pole, that is, they make an angle (28°37') with the horizon, equal (approximately) to the latitude of Delhi, and are parallel to the earth's axis. The quadrants (M K G E D, figure 35) are at right angles to the gnomon, and, therefore, the circles, of which they form part, are parallel to the plane of the equator. These quadrants have each a radius of 49·5 feet, and are graduated on each edge in hours, degrees and minutes,¹ the scales on the northern edges being marked in English and those on the southern edges in Indian symbols. The edges of the gnomon are marked with scales of tangents, as already explained (page 36, see figures 34 and 35). The shadow of the edge of the gnomon on the quadrants gives the local time. In figure 40 the time is about ten minutes to four in the afternoon. The sun's declination is found by observing which part of the gnomon's edge casts its shadow on one of the edges of the corresponding quadrant (see page 36).

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³ For the theory of the instrument see p. 36.

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¹ Jai Singh gives 18 cubits as the radius and one minute as equal to a barleycorn and-a-half. See page 13. The time scales are on the upper surface of the quadrants, and the degree scales on the extreme edges. The European symbols were, probably, introduced at the restoration in 1910.

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In the mass of masonry work that supports the east quadrant is a chamber which contains the *Shasthāmśa Yantra*. This is a large graduated arc 60 degrees in length, built in the plane of the meridian; and through a small orifice near the top of the quadrant the sun, as it passes the meridian, shines on the arc and indicates its meridian altitude, from which its declination can be directly deduced. The chamber was closed up when the observatory was restored in 1910.

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On the top of the gnomon is a circular pillar, which was probably used originally for rough azimuth observations, but which is now surmounted by a small sundial of the European type. This was probably constructed in 1910: the pillar, but not the dial, appears in the Daniells' drawings (figures 43 and 44).²

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² In December last a Trigonometrical Survey party was using the top of the gnomon as a point of observation and found the dial in the way. The pillar, as it was originally designed, was exactly suitable for their purpose.

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The lower part of the structure is now, more or less permanently it seems, below the water level of the locality. The height of the water varies³ but for a great part of the year it covers the lower part of the quadrants and the steps and prevents access to the west quadrant altogether; and it makes the structure useless for astronomical purposes. If the instrument is to be saved, means must be taken to prevent the water percolating to the foundations.

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³ In January 1916 its maximum depth was about 4 feet, while at the end of August it was 3 feet deeper.

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According to Jai Singh, the *Samrāṭ Yantra* was built of stone and lime.⁴ Hunter and Thorn say that the edges of the gnomon and quadrants were of white marble, and von Orlich speaks of marble staircases (see page 48). The quadrants are now faced with lime, but the time graduations are well marked with a soft black stone, neatly inlaid into the face of the quadrant. The graduations on the edges of the gnomon are scratched into the lime plaster surface and are becoming obliterated.

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⁴ See Preface to the *Zij Muhammad Shāhi*, p. 13 above.

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MISRA YANTRA

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SAMRAT YANTRA

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JAI PRAKASH

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RAM YANTRA

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DELHI OBSERVATORY.

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SCALE

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Fig 44.

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Fig 43.

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Fig 46.

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Fig 45.

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Figs 43 & 44 DELHI OBSERVATORY AFTER DRAWINGS PUBLISHED IN A.D. 1815.

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Figs 45 & 46 DELHI OBSERVATORY IN A.D. 1915.

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Survey of India Offices, Calcutta, 1915.

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An examination of the Daniells' drawings and recent photographs (see figures 43-46) shows that only minor alterations have been made during the last hundred years. There is a slight difference in the entrance to the gnomon steps; in the old drawings is shown a set of subsidiary steps to the right of the main steps on the gnomon; and there was formerly no dial at the top of the gnomon.

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38. The Jai Prakāś consists of two complementary concave hemispheres, situated immediately south of the Samrāṭ Yantra. Their structure is best seen in plates XVIII and figures 41 and 42. Theoretically, only a single hemisphere is necessary, but, to facilitate observation, pathways are cut into the surface; and the second Jai Prakāś is so constructed that the two instruments together show the complete surface. Cross wires were, originally, stretched across the hemispheres north to south and east to west, and the shadow of the intersection of these wires on the concave surface of the hemisphere indicated the position of the sun. The surface of the hemisphere is marked with altitude and azimuth circles, the tropics and intermediate circles (declination parallels), etc., so that the position of the sun can be directly read off. Also there are ‘circles of the signs of the zodiac,’ by which the particular sign on the meridian is indicated by the position of the sun's shadow.¹ In the Delhi instruments the cross wires have been discarded, although the pins to which they should be fastened are still there; and iron rods (2 inch galvanized piping) have been fixed at the centre of each Jai Prakāś. The pipes should be removed and the cross-wires replaced.

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¹ For a more detailed account of the theory of the instrument see p. 37.

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The descriptions given by Hunter and Thorn seem to indicate that there was, a century ago, only one Jai Prakāś. Hunter's words are: “Between these two buildings (i.e., the Rām Yantra), and the great equatorial dial is an instrument called Shamlah. It is a concave hemispherical surface, formed of mason work, to represent the interior hemisphere of the heavens. It is divided by six ribs of solid work and as many hollow places; the edges of which represent meridians at the distance of fifteen degrees from one another. The diameter of the hemisphere is twenty-seven feet five inches.” Thorn uses the same phraseology. The old drawings and photographs are ambiguous on this point, but they show that the original structure has been altered considerably. Probably there were two complementary instruments originally, but one of them had disappeared.

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39. The Rām Yantra consists of two large circular buildings, complementary to each other, situated south of the Jai Prakāś. Their general structure is best seen in figures 39, 41, 47-49 and in the plates XIII and XVII. Each consists of a circular wall and a pillar at the centre. The height of the walls and pillar, from the graduated floor, is equal to the inside radius of the building measured from the circumference of the pillar to the wall, viz., 24 feet 6½ inches, and the diameter of the pillar is 5 feet 3½ inches. The walls and floor are graduated for reading horizontal (azimuth) and vertical (altitude) angles. To facilitate observation the floor is cut up into thirty sectors, with the spaces between of the same angular dimensions as the sectors, viz., six degrees. The graduated sectors are supported on pillars three feet high, so that the observer can ‘place his eye’ at any point on the scale. The graduated walls are, similarly, broken up by openings, at the sides of each which are notches for placing sighting bars. At Delhi there are no such bars in evidence but at Jaipur they are faced with brass and carefully graduated. At Jaipur the central

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FIG. 47. RĀM YANTRA INTERIOR.

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pillar is replaced by an iron rod. At Delhi the pillar is graduated by vertical stripes see figure 48), each six degrees in width, and these are necessary, as a point on the top of the edge (not the centre) of the pillar is the centre for which the altitude graduations on the corresponding sector and portion of the wall are made. The old descriptions and drawings show that no important structural alterations have been made during the last century. The Daniells’ picture (figure 44), however, apparently shows a different entrance to the north Rām Yantra.

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PLAN

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SAMRĀT YANTRA, DELHI.

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ARCH OF A BRIDGE

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[Figure: SOUTH ELEVATION SAMRAT YANTRA, DELHI.]

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SECTION OF THE TOWER

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SCALE OF 10 FEET

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40. To the north-west of the Samrāṭ Yantra, and some 140 feet away, is the Miśra Yantra, or ‘mixed instrument,’ so named because it combines in one building four separate instruments. Of these the Niyat Chakra occupies the middle of the building, and consists of a gnomon with two graduated semicircles on either side (figure 50). These semicircles lie in planes inclined to the plane of the Delhi meridian at angles of 77° 16′ W., 68° 34′ W., 68° 1′ E. and 75° 54′ E.¹

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¹ These are the angles given by the Paṇḍits, but according to the measurements of the engineers, who prepared the plans the angles are 77° 18′, 69° 50′, 69° 42′ and 77° 22′. They are difficult to measure accurately.

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The semicircles may be said to correspond to meridians at places whose longitudes differ from Delhi by these angles, and tradition names Greenwich observatory² and the observatory³ at Zurich, “Notkey a village in Japan where there is an observatory, latitude 43° 33′ N. and Longitude 145° 17″ E. of Greenwich,” and “Serichew a town in the Pic Island in the Pacific Ocean east of Russia latitude 48° 6′ and longitude 153° 12′ E.”

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² This implies that the longitude of Delhi was taken as 77° 16′ E. of Greenwich. It is really 77° 13′ 5″, Zurich observatory is 8° 34′ E. of Greenwich.

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³ It may be noted that Greenwich observatory was founded in 1675, some 50 years before that at Delhi was built, but that Zurich observatory did not come into existence until 1759, some sixteen years after Jai Singh's death.

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Let *AB* (figure 36) be the edge of the Delhi gnomon, and *ABD* in the plane of the Delhi meridian. Let *ABE* make an angle δ with *ABD*, then *ABE* represents a meridian at a place whose longitude difference from Delhi is δ. Let *CX* denote the direction of the sun when it is in the Delhi meridian, then the arc *DP* will measure its declination; and if *CX₂* be the direction of the sun when in the plane *ABE*, then *EQ* will measure its declination. On the Niyat Yantra the semicircle *ABD* is not marked, but *ABE* corresponds to one of the masonry semicircles, each of which is graduated north and south from E for the purpose of observing declinations.

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On either side of the Niyat Yantra, and joined to it, is half of an equinoctial dial, constructed on the same principle as the large Samrāṭ Yantra. On the west side of the building is a second quadrant, the face of which is horizontal instead of being parallel to the axis. It is called the Agrā Yantra or ‘amplitude instrument,’ and its use does not seem to have been understood by the restorers. Hunter makes no mention of this.

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On the east wall of the building is a graduated semicircle called Dakṣiṇo vṛtti Yantra, used for obtaining meridian altitudes. The north wall of the Miśra Yantra is inclined to the vertical at an angle of 5 degrees (figure 51), and is marked with a large graduated circle. This is called the Karka Rāśi Valaya, or ‘Circle of the sign of Cancer.’ As the latitude of Delhi observatory is 28° 37′ 35″, and the obliquity of the ecliptic is 23° 27′ 5″ nearly, the zenith distance of the sun, when in Cancer, is 5° 10½′, approximately, and the sun then shines over the north wall for a short period, and the shadow of the centre pin falls on the graduated circle. This may be the northern dial referred to by Jagannāth (see page 39).

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41. In the front of the Miśra Yantra is a platform 47 feet by 43 feet, on which are traces of a quadrant of 20 feet radius. This platform was probably used for making measurements when the instruments were being constructed or repaired.

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To the south-west of the Miśra Yantra are two pillars 17 feet apart, and the line joining their centres points 35° E. of north. These are mentioned in none of the accounts of the observatory. If they were part of the original observatory, they probably supported one of Jai Singh’s instruments, such as are now found at Jaipur (see figures 28 and 29).

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Hunter states that, to the west of the Miśra Yantra and close to it was a wall in the meridian with double quadrants. Jagannāth, Jai Singh’s assistant, recorded ¹ that, in the year 1651 ² of the Śalivāhana era, “with this instrument, the latitude of Indraprastha ³ was found to be 28° 39′ north, and the maximum declination 23° 28′.”

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¹ See page 3 and Garrett page 36.

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² A. D. 1729.

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³ Delhi.

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To the west of the Samrāṭ Yantra is a small building (a chowkidar’s house) on which is fixed the Jaipur flag. There is a tree south-east of the eastern Jai Prakāś that partially overshadows that instrument. The tree should, of course, be removed. The whole observatory is enclosed by a mud wall about six feet high, with an entrance on the west side.

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42. History. The observatory at Delhi was the first one built by Jai Singh, and it is here that the principal observations were made, which were to form the basis of his new tables, the Zij Muhammad Shāhī. There is some uncertainty about the date of construction. Paṇḍit Gokal Chand gives A.D. 1710, and Syed Aḥmad Khān gives 1724. The latter states that the observatory was built “in accordance with the orders of the Emperor Muhammad Shāh, in the seventh year of his reign,⁴ corresponding to the year 1137 of the Hijira” (=A.D. 1724-5).⁵

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⁴ Muhammad Shāh ascended the throne in 1719 (October 9th).

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⁵ Thorn says: “The third year of the reign of Mohammad Shāh or 1724.

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Jai Singh tells us ⁶ that he himself represented the question of preparing new tables, to the Emperor, who encouraged him to proceed. “To accomplish the exalted command he had received, he (Jai Singh) bound the girdle of resolution about the loins of his soul, and built here (at Delhi) several of the instruments of an observatory.” This seems to indicate that the construction was started *after* Muhammad Shāh ascended the throne. Also, Jai Singh himself tells us that seven years were spent in preparing the tables. In 1719 Jai Singh was appointed the Emperor’s lieutenant at Agra. Jagannāth records observations made at Delhi in A.D. 1729. The facts seem to point to 1724 as about the date of the founding of the Delhi Observatory.

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⁶ See page 11.

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Jai Singh tells us that, at first, he constructed at Delhi brass instruments of the astrolabe type in accordance with the Muslim books.⁷ These he found to be unsatisfactory, and, therefore, he constructed “instruments of his own invention, such as Jai Prakāś and Rām Yantra and Samrāṭ Yantra . . . of stone and lime of perfect stability, etc.” In Jai Singh’s time, therefore, the observatory probably consisted of the Samrāṭ Yantra, the Jai Prakāś, the Rām Yantra, a mural quadrant, and some metal instruments. Of the present buildings, possibly, the Miśra Yantra was added by Madhu Singh, “who inherited no small portion of his father’s love of science.”¹

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⁷ See page 12.

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¹ Tod ii, 372.

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Fig. 49. THE RAM YANTRA, DELHI, SOUTH BUILDING.

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Fig. 51. MISRA YANTRA, DELHI, FROM THE NORTH.

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Fig. 47. THE RAM YANTRA, DELHI, NORTH BUILDING.

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Fig. 50. MISRA YANTRA, DELHI, FROM THE SOUTH.

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43. Early descriptions. There are fairly numerous references to the Delhi observatory in the accounts of travellers of the eighteenth and early part of the nineteenth century, and some of these are worth recording. Father Claude Boudier and another priest passed through Delhi in 1734 on their journey to Jaipur (see page 6), and took observations of latitude and longitude at the observatory at Delhi. Unfortunately they have left on record no description of the observatory or the instruments.

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In 1795 Franklin, in his description of the city of Delhi,² wrote of the observatory: “It was built in the third year of the reign of Muhammad Shāh, by the Rajah Jeysing, who was assisted by many persons, celebrated for their science of astronomy, from Persia, India and Europe; but died before the work was completed, and it has since been plundered and almost destroyed by the Jeits, under Juhwaher Singh.”

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² An Account of the present State of Delhi. By Lieut. Franklin. Asiatic Researches, vol. iv, 1895, p. 431. Muhammad Shāh’s reign commenced in 1719, and Jai Singh died in 1743.

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In 1799 W. Hunter published³ a fairly complete account of the Delhi observatory. The list of buildings and the descriptions he gives show that, to the west of the Miśra Yantra and close to it was a wall in the plane of the meridian, on which was described “a double quadrant having for centres the two upper corners of the walls . . . . One degree on these quadrants measured 2·833-inches.”⁴ Also, in describing the Miśra Yantra, he makes no mention of the third quadrant (Agra Yantra) on the west side. Referring to the Samrāṭ Yantra he states “It is built of stone, but the edges of the gnomon and arches, where the graduation was, were of white marble, a few small portions of which only remain.”

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³ Asiatic Researches, v, 1799, 177f.

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⁴ He does not mean that he measured correctly to a thousandth of an inch, but that it was approximately 2¾ inches. The radius was consequently about 13½ feet.

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In 1803 Major William Thorn visited Delhi, and, later, gave a description⁵ of the observatory. His description, however, is simply a summary of Hunter’s and he gives no additional information whatever, although he is sometimes quoted as an authority.

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⁵ Memoir of the War of India conducted by General Lord Lake in 1818, p. 171.

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Soon afterwards, the Daniells gave two illustrations⁶ of the chief features of the observatory. These are here reproduced (figures 43 and 44) and they show that during the last hundred years very little alteration has really taken place; but they show some small differences, which have already been mentioned.

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⁶ Oriental Scenery, 1815, part v, plates XIX and XX. The original drawings for these plates must have been made about A. D. 1794.

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In 1843 von Orlich visited Delhi and made the following notes about the observatory: "It lies in the midst of many ruins; but it was never completed and has been, unhappily, so wantonly dilapidated by the Juts that the shattered ruins alone are to be seen. However, enough remains to show the plan of this fine building; the colossal sun-dials and quadrants, which rest upon large arches, are formed of red sandstone and bricks, and the ascent to them is by handsome winding marble stair cases."¹

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¹ *Travels in India*, London, 1845, p. 49. (The account is not reliable, and, i am inclined to think, von Orlich never visited the observatory; but what he says is the sort of thing that occurs in many guide books.)

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Next comes Syed Aḥmad Khān's description,² which was translated by Garçin de Tassy.³ This account is not very reliable, but the original work contains some rough, but valuable, drawings of the instruments. We read: "Now this observatory has fallen into ruin; all the instruments are broken, and all traces of the lines of division have disappeared, etc."

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² *Āthār al-Sanādīd* 1852. Reprinted 1876.

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³ *Journal Asiatique*, V. xv, 1860, 536f.

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Later writers on Delhi give brief notices of the observatory with, in two cases,⁴ interesting photographs.

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⁴ Carr Stephen.—The *Archæological and Monumental Remains of Delhi*, 1876; and H. C. Fanshawe, *Delhi, Past and Present*, 1902.

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44. Past Restorations. Syed Aḥmad Khān tells us that, in 1852, the Raja of Jaipur partially restored the Samrāṭ Yantra, at the request of the Archæological Society of Delhi; and, in the Proceedings of the Delhi Archæological Society of the 6th January 1853, we read: "It having been stated that the large gnomon of the Junter Munter had been repaired at a cost of Co.'s Rs. 442-1-10, leaving a balance of Co.'s Rs. 157-14-2 of the sum presented to the Society by the Rajah of Jeypore, for the repairs of that Observatory, and this being much too small a sum to enable the Society to complete the repairs, or even to build around a compound wall, which is absolutely necessary, for the security of the remains from further dilapidation, it was unanimously resolved that the Agent to the Lieutenant-Governor, Delhi, be requested to make known to the Rajah of Jeypore, through the proper authorities, the inability of the Society to complete the contemplated work, without further funds." For many years nothing further was done. In 1910, His Highness, the present Mahārāja of Jaipur, sanctioned the restoration of the observatory at Delhi, and the work was completed in 1912. Paṇḍit Gokal Chand was placed in charge of the astronomical part of the restoration, which was carefully carried out. The work comprised the restoration of the buildings, the regraduation of most of the scales, and, in the case of the Jai Prakāś, practically the reconstruction of the whole instrument. Most of the facings and the graduations were done in lime plaster, but the main graduations on the quadrants of the Samrāṭ Yantra are in a soft black stone, very neatly inlaid in the surface of the quadrants. The graduations in lime are already becoming obliterated. On the top of the gnomon of the Samrāṭ Yantra a sun-dial of European type was erected.

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On each instrument a tablet giving the name of the instrument, the date of restoration, etc., was placed. Some of these were done in marble and some in plaster. Several of the latter are already destroyed.

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PLAN

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RAM YANTRA

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SECTIONAL ELEVATION ON A B C

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GROUND

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Feet

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PLAN

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SECTION ON A. B.

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12 FEET 16

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SIDE ELEVATION

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Misra Yantra

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BACK ELEVATION

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FRONT ELEVATION

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Fig. 1.

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Fig. 2.

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45. Future Restorations. The Delhi Observatory buildings are worthy of permanent preservation, not only on account of their scientific and historic value, but as monuments to one of the most brilliant and remarkable princes of India, and as forming a dignified feature of the new Imperial City.

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The grounds surrounding the buildings should be enclosed by a low wall, and the grounds themselves should be ornamented only by a grass lawn. There should be neither trees nor shrubs, but there would be no objection to flower beds at a sufficient distance from the buildings. The buildings should be put into good order without interfering in any way with their present structure. The present pink colouring should be removed and a natural lime-plaster tint substituted. The graduations should in all cases be made in some more permanent substance than lime plaster. At Jaipur marble and sandstone are both used, and at Benares the latter only. Marble, or some other suitable stone, should be employed.

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The Samrāṭ Yantra (figure 40, etc.) is the most important of the instruments, and every effort should be made to preserve it permanently. Its foundations are in a rectangular excavation, which is now partially filled with water. Apparently the bottom of this excavation is lower than the surrounding water level, and, consequently, the water percolates and covers the lower portions of the instrument. Not only is it damaging the structure, but it makes it useless for purposes of present observation. To get rid of the water is a problem for the engineers, and possibly they will decide to ‘concrete’ the whole of the lower part of the excavation, and install a small electric pump. Unless some such means to exclude the water are taken, the chief instrument of the observatory will be utterly ruined. When the water has been excluded, the chamber containing the Shashṭhāṁśa Yantra, described above (page 42), should be opened out, and the instrument put in working order.

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The main graduations on the quadrants of the Samrāṭ Yantra are suitable,¹ and need not be restored at present, but the graduations on the edges of the gnomon need restoration badly. This necessitates the edges being refaced with marble or some suitable stone. The small dial on top of the pillar, that is at the top of the gnomon, should be removed. It is of no use where it now is and it prevents the pillar, on which it is placed, being used for its legitimate purpose. The sun-dial might be placed somewhere, out of the way, in the grounds. The space round the pillar is hardly sufficient for working purposes, and it would perhaps be as well to reduce the diameter of the pillar, or to place around it a railing for protection. (An examination of the Jaipur gnomon shows that some such arrangement would not be in opposition to Jai Singh’s idea.) The top of the pillar should be graduated, as most probably it was originally, for rough azimuth observations, and should be made perfectly level.

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¹ It was a mistake, I think, to introduce European measures and symbols, and I should like to see the edges, faced with marble as originally they were, and the old graduations replaced.

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The position is one for observation and could even now be used, in the spirit of the original design, for many purposes.

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The graduated parts of the Jai Prakāś require refacing either with marble or other suitable stone. The original was in lime plaster, but it did not last very long; and in 1910 the facing was again done in lime plaster, but the graduations are already becoming obliterated (see figures 32 and 33). The central iron rod (galvanised piping) should be removed and the cross wires replaced.

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The graduation (in lime plaster) on the walls of the Rām Yantra are not so exposed, and consequently not so liable to deteriorate as those in the Jai Prakāś. The walls of the Rām Yantra at Jaipur are in marble, but there the instrument is much smaller than that at Delhi.

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The Miśra Yantra graduations are all in lime plaster, and should all be done in stone or marble. This means refacing the edges of the gnomon, and the semicircular meridians, and inlaying on the quadrants, etc.

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The mural quadrant described by Hunter (see page 47), and no longer in existence, might be rebuilt. It was originally to the west of the Miśra Yantra, but the space is somewhat limited there. There are examples at Jaipur (figure 56), Ujjain (figure 62), and Benares to serve as models.

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The probable use of the two pillars marked on the general plan has been already explained (page 46). A brass instrument such as the Unnataṁśa Yantra, or large Yantra Rāj at Jaipur might be replaced.

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The tablets on the instruments should be restored and revised, and they should, of course, be placed where they can easily be read¹; and should give the name of the instrument, its uses, dates of construction or restoration, the names of the original designer (in most cases Jai Singh) and the restorers. The English versions should be revised by a European astronomer.²

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¹ Two of the present tablets are too distant to be read with ease.

c10.120

² The following is an example of those now on the instruments :— "Kark Rashi Balay Yantra, Restored A.D. 1910. Tested by Jotish Gokal Chand Bhawa, for finding the longitude of the sun wh n the Cancer or the point 90 in the Faliptic comes over the plane of Meridian."