Points of Interest

The Telescope in the Court

The giant stone instruments of Jaipur and Delhi are often presented as an ancient observatory, and sometimes as the work of a king who never heard of the telescope. They were built in the 1720s and 1730s by a ruler who had telescopes, sent a mission to Europe for its astronomical tables, and chose masonry anyway — for a reason that had to do with measuring, not looking.

The myth

Visitors to Jaipur, Delhi or Ujjain meet the instruments first: a staircase-shaped sundial rising higher than the surrounding buildings, bowls sunk into the ground and marked with the coordinates of the sky, walls and arcs of plastered stone laid out in a courtyard like sculpture. Travel listings and heritage pages routinely describe them as an "ancient astronomical observatory," or place them among the "astronomical instruments of ancient India," as if they were a surviving piece of the world of Aryabhata and Varahamihira.

A second version, told less often but with more condescension, runs the other way. In this telling the instruments are impressive precisely because they are obsolete: a king in the eighteenth century, cut off from Europe, pouring stone into giant versions of medieval tools while the telescope had already remade astronomy elsewhere. Monumental, and a dead end.

The two versions disagree about almost everything except one assumption. Both take the stone instruments to be what astronomy looks like when you do not have a telescope.

Not ancient: a building programme of the 1720s and 1730s

The observatories were built by Sawai Jai Singh II (1688–1743), ruler of Amber and the founder of the planned city of Jaipur, which replaced Amber as the capital in 1733. He raised five of them in the second quarter of the eighteenth century, at Shahjahanabad (Delhi), Jaipur, Ujjain, Mathura and Varanasi, as described in S. N. Johnson-Roehr's survey of the sites in the Handbook of Archaeoastronomy and Ethnoastronomy (2015).

The dates within that programme are less certain than the monuments suggest. The Delhi observatory came first: the preface to Jai Singh's astronomical tables, as translated in G. R. Kaye's study The Astronomical Observatories of Jai Singh for the Archaeological Survey of India, indicates that Delhi was completed and in use before the others were begun. For Jaipur, the standard reference accounts give construction from 1728 to 1734; at least one popular history gives 1724 to 1727 instead. Those cannot both be right, and this piece does not choose between them.

What is not in doubt is the century. The largest instrument at Jaipur, the Samrat Yantra — in effect an enormous equinoctial sundial — was being set out roughly a hundred and twenty years after Galileo turned a telescope on Jupiter. Whatever the stones are, they are not a relic from before the telescope. They were built in full knowledge of it.

What the king said was wrong with brass

Jai Singh left an account of his motives in the preface to the tables that came out of the observatories, the Zij-i Muhammad Shahi, named for the Mughal emperor Muhammad Shah. In Kaye's translation, he describes "finding that brass instruments did not come up to the ideas which he had formed of accuracy, because of the smallness of their size, the want of division into minutes, the shaking and wearing of their axes."

Every item on that list is a mechanical complaint. A small circle cannot be finely divided; a scale not divided into minutes cannot be read to a minute; an axis that shakes or wears moves the reading. The preface then applies the same diagnosis to the ancients, arguing that the astronomers of the past had been limited by the same defects. His answer was to build instruments that could not shake, would not wear, and were large enough that a minute of arc became a physical distance a person could see. The preface describes the great sundial's semi-diameter as "eighteen cubits," and states that "one minute on it is a barley corn and a half."

Modern descriptions translate that ambition into a figure that is often repeated: the smallest division on the Jaipur Samrat Yantra corresponds to about two seconds of time. That is a statement about the graduation of the scale — how finely it is marked — rather than a measured accuracy for any observation made with it, and it is worth reading that way. The published dimensions of the instrument also vary between sources, from 73 feet in one popular account to 27 metres (about 88 feet) in others. The instrument is real; the numbers attached to it have been rounded and copied more often than they have been checked.

The telescope that came to court

Jai Singh was not isolated from European astronomy. He cultivated it. The Jesuits working in India were his channel. According to the translated preface, he sent "several skilful persons along with Padre Manuel" to Europe, and they brought back "the new tables which had been constructed there thirty years before and published under the name Lir." Kaye identified these as the Tabulae Astronomicae of the French astronomer Philippe de La Hire. One annotated edition of the preface identifies "Padre Manuel" as the Portuguese Jesuit Father Figueiredo, who, it suggests, travelled "in 1728 or 1729." Other accounts record Jai Singh inviting the French Jesuit Claude Boudier from Chandernagore, and, in 1737, negotiating with the Viceroy of Goa for the passage of two more Jesuit mathematicians, Anton Gabelsperger and Andreas Strobl, to Jaipur.

He compared the European tables against his own observations and was not impressed. The preface reports that "there was an error in the former in assigning the moon's place of half a degree." A half-degree error in the Moon's position is roughly the width of the Moon itself.

He also had telescopes. The historian of astronomy S. M. Razaullah Ansari, in a published conversation with S. Irfan Habib, describes a court record noting a telescope presented by Jai Singh to the emperor Muhammad Shah. Later popular accounts go further and credit Jai Singh with telescopic observations — one lists Venus and Mercury, the rings of Saturn and sunspots, others add the satellites of Jupiter. The lists do not agree with one another, and this piece could not trace any of them to a primary record. That he had the instrument is well attested. What he saw with it is not.

Looking is not measuring

So why build in stone? Ansari's answer, in the same conversation, is the most useful sentence in the whole story: "The telescopes were only for looking, not for measuring. For the measurement there should be a crosswire." In his account, Jai Singh judged that the telescopes available to him could not give a good reading, and that his large instruments could.

That judgement was not naive. The telescope of the early seventeenth century was a device for discovery — moons, phases, spots — and positional astronomy, the business of fixing where things are to a fraction of a minute, needed something more. The missing piece had been invented in England: the Linda Hall Library's account of William Gascoigne describes how, before his death in 1644, he found that replacing the naked-eye sight of a quadrant or sextant "with a telescopic sight containing cross-hairs" greatly improved accuracy, and devised a micrometer of two wires, one adjustable by a screw. Gascoigne was killed at Marston Moor in the English Civil War; his crosshair sights were later adopted by John Flamsteed, the Astronomer Royal, for the sextants and mural quadrant at Greenwich.

By Jai Singh's time, then, measuring telescopes existed in European observatories. But the telescopes that travelled to a court in Rajasthan through Jesuit hands were, on Ansari's account, of the looking kind. Faced with an instrument that showed more but measured nothing, and a masonry sundial that showed nothing new but could be read against a scale marked in small divisions, a ruler whose stated problem was reading positions accurately chose the scale. The gap between Jaipur and Greenwich was not ignorance of the telescope. It was the absence of a fine crosswire, a precision screw, and the instrument-making trade that produced them.

There is a second gap, and it is harder to close. Ansari notes that when Jesuits came to Jai Singh's court, their reaction was, in his paraphrase, that astronomy had moved on and the king was still building observatories. The words are Ansari's summary rather than a recorded remark, and they should be read as such. Whether the Zij itself absorbed European theory is also contested: popular accounts say Jai Singh set the French tables aside, while the scholar Virendra Nath Sharma, author of Sawai Jai Singh and His Astronomy, has published a study devoted specifically to the relation between the Zij's tables and de La Hire's. The record is not settled, and it should not be summarised as though it were.

Why the truth is the better story

The ancient-observatory version flatters the instruments by removing them from their century, and the obsolete-king version dismisses them by keeping them there. Both treat the stones as a monument to not knowing.

The documented story is about a man who knew a great deal and made a choice. Jai Singh had telescopes. He had a Jesuit network and a mission to Europe. He had de La Hire's tables, fetched by his own mission, and he checked them and found them wrong about the Moon. His own written reason for building in stone is an engineer's list of failure modes — small circles, coarse divisions, shaking axes. And the instrument that would have changed his calculation, a telescope fitted to measure rather than to look, existed in Europe but did not, on the best available account, reach his court.

The result is a more interesting kind of dead end than the myth offers. Ansari's verdict is that the translations were archived, with no commentaries and no successors. The observatories were restored in 1876 and 1901 and again in 2006, and Jaipur's was inscribed as a World Heritage Site in 2010. They survive as the most complete record of one question — how far can careful naked-eye measurement go if you make the instrument big enough? — asked seriously by someone who knew there was another answer, and could not yet get hold of it.

On sources. The five observatory sites and their placement in the second quarter of the eighteenth century are from S. N. Johnson-Roehr, "Observatories of Sawai Jai Singh II," in Handbook of Archaeoastronomy and Ethnoastronomy (Springer, 2015), as given in its published abstract. All quotations from Jai Singh's preface to the Zij-i Muhammad Shahi — the defects of brass instruments, "eighteen cubits," "a barley corn and a half," "Padre Manuel," "published under the name Lir," and the half-degree lunar error — are from the English translation reproduced in G. R. Kaye, The Astronomical Observatories of Jai Singh (Archaeological Survey of India), in the digitised text held by the Internet Archive; Kaye's identification of "Lir" with de La Hire's Tabulae Astronomicae is his. The suggestion that Father Figueiredo travelled "in 1728 or 1729," and that the Delhi observatory preceded the others, is from an annotated edition of the preface; the identification is probable, not certain. Boudier's invitation and the 1737 negotiation for Gabelsperger and Strobl are from secondary accounts of Jai Singh's Jesuit contacts. The Jaipur construction dates of 1728–1734, the restorations of 1876, 1901 and 2006, the 2010 World Heritage inscription, and the 27-metre height are from standard reference accounts of the Jaipur site; the alternative dates of 1724–1727, the 73-foot height, the two-second division and Jaipur's 1733 replacement of Amber are from Live History India's account of the observatory. Where these disagree, the disagreement is reported rather than resolved. Ansari's remarks on telescopes, crosswires, the Jesuits' reaction and the absence of successors are from "S. Irfan Habib in conversation with S. M. Razaullah Ansari," published by Sahapedia; the Jesuits' reaction is Ansari's paraphrase, not a recorded quotation. The list of telescopic observations attributed to Jai Singh is from a Muslim Heritage article by Zakaria Virk (2019), citing A. Y. al-Hassan's Science and Technology in Islam; other accounts give different lists, and none was traced to a primary record. Gascoigne's crosshair sight and micrometer, the quoted phrase, his death at Marston Moor in 1644 and Flamsteed's adoption of his sights at Greenwich are from the Linda Hall Library's Scientist of the Day account. The reading of the two-second figure as a graduation rather than an accuracy, and the argument that the decisive gap was measuring hardware rather than knowledge, are this publication's interpretation. The travel and heritage descriptions of the sites as "ancient" are quoted from public listings of the Ujjain observatory and a heritage article titled "Astronomical Instruments of Ancient India: The Jantar Mantar and Beyond"; the "obsolete" reading is characterised here as a recurring framing rather than attributed to any single author.