Maharaja Sawai Jai Singh II (1686-1743), was the ruler of the Rajput State of Amber in India. A feudatory of the Mughals, he received the title of 'Sawai' (one and a quarter) from Emperor Aurangzeb, who declared him a quarter superior to his famous forebearer Mirza Raja Jai Singh (d. 1667) after he captured the Fort of Vishalgarh from the Marathas in 1701. The title was officially recognized by an Imperial Edict in 1712, and, to commemorate it, the rulers of Jaipur began the practice of flying two flags, one full and one quarter-sized. After the death of Aurangzeb in 1707, the Mughal Empire went into a decline and the Delhi Court became a hotbed of intrigues and treacherous politics. It wasn't until 1719, when, after surviving assassination attempts and other sundry opposition, the nineteen-year old Muhammad Shah became the Emperor, that some sort of stability was achieved. This lasted for the next twenty years until the Afghan invader Nadir Shah sacked Delhi in 1739 and, amongst other loot, carried away the famous Peacock Throne. The shrewd and opportunistic Jai Singh managed to retain his political importance during these turbulent times. His accomplished diplomacy had kept him in Aurangzeb's good graces and he remained a favorite with Muhammad Shah too. It was on his instigation, that the new Emperor abolished the hated Jaziya tax imposed on the Hindus. After bringing to the Emperor's notice some astronomic discrepancies that possibly affected the timings of Hindu and Muslim holy events, and expressing his desire to correct these, he also received Imperial backing for building his Astronomy Observatories at Delhi, Jaipur, Varanasi, Ujjain, and Mathura. In return, as a tribute to his Mughal patron, he titled the astronomical work he completed in 1728 as 'Zij-e-Muhammad-Shahi (Muhammad Shah's astronomical tables). That same year, he also built his new, magnificently designed capital, Jaipur, about 200 km southwest of Delhi, and constructed by combining the aspects of the ancient Hindu treatise on architecture, the Shilpa Shastra, and plans of many European cities of the period with Jai Singh's own ideas. Jaipur, which was built on the grid system with nine rectangular zones corresponding to the nine divisions of the universe, and had different zones allotted to different professions, boasted 119 feet wide main streets that were perpendicularly intersected by 60 feet wide auxiliary streets, which were further honeycombed by 30 feet wide lanes and 15 feet wide by-lanes. Beautiful, harmonized buildings, and shady trees, lined the streets, and the city was well-provided with a water passage and wells. The European travelers of the time, like the Frenchman Louis Rousselet, and the English bishop, Heber, were greatly impressed by his unparalleled excellence in city-planning.
Astronomy, however, was his grand passion. He was a scholar, with an eclectic collection of astronomical manuscripts and tables from Arabia and Europe, that included the Englishman John Flamsteed's 'Historia Coelestis Britannica', the Portuguese Pere de la Hire's 'Tabulae Astronomicae', the Turkish royal astronomer, Ulugh Beg's tables 'Zij Ulugh Begi', and the Greek Ptolemy's 'Almagest'. With the help of Pandit Jagannath, a multilingual Marathi Brahmin, he had these treatises translated into Sanskrit and they were given Sanskrit names - Ptolemy's treatise became 'Siddhantasurikaustubh', Ulugh Beg's tables 'Turusurni', and la Hire's tables 'Mithiajeevachayyasurni'. He also acquired telescopes from Europe, prior to which he had conducted observations using astrolabes and other instruments. With these, he had detected the discrepancies in the earlier astronomy tables, that had happened due to changes in the positions of the heavenly bodies.
Jai Singh's observatories were called 'Jantar Mantars', which in Sanskrit roughly translates to 'The Formula of Instruments'. The first one was built at Delhi in 1724, the second at Jaipur in 1734, and the other smaller ones at Mathura, Ujjain, and Varanasi, between 1732 and 1734. These monumentally grand, surrealistic structures, with their remarkable geometric shapes, are themselves the astronomical instruments, outfitted with drafting devices, grid indicators, and are so highly sophisticated that they are capable of exactly measuring planetary positions, as well as reading time precise to one second. They were built with the assistance of the Bengali Pandit, Vidyadhar Bhattacharya (also the engineer of Jaipur City), and are based on Ulugh Beg's large 15th century instruments at Samarkhand. Although smaller, futuristic instruments like the telescope and newer-type of observatories in Paris and Greenwich were revolutionizing contemporary Europe, Jai Singh had more faith in the accuracy of his huge masonry structures. He also himself designed some of the instruments, like the 'Samrat Yantra', 'Ram Yantra', and 'Jai Prakash Yantra'.
The 'Samrat Yantra' is a gigantic 90 feet high and 148 feet wide sun-dial, north-south coordinated and angled at 27 degrees, the latitude of Jaipur, and outfitted with finely calibrated quadrants on which the movement of the sun's shadow (falling on the western ramp before noon and on the eastern ramp in the afternoon) can be carefully charted, to not only measure the local time to an accuracy of half a minute, but also precisely note zenith distances, meridian pass time, and the celestial latitudes. The Samrat Yantras in the five observatories are each dissimilar in form, in order to make the hypotenuse of the high ramp (gnomon) and the adjacent quadrants, perfectly parallel to the earth's axis and the equator respectively.
The 'Ram Yantra' is a high column inside a marked container, which is capable of accurately gauging the altitude and azimuth (the azimuth of a celestial body is the angle between the vertical plane containing it and the plane of the meridian) of planets.
The most fascinating of all is the 'Jai Prakash Yantra', which consists of two large, bowl-shaped, complementary, marble hemispheres, that have planetary latitude and longitude markings, and are deep-set in the ground with channels for allowing the instrument reader access to other parts of the hemispheres. A small pointer on a wire is hung over the center of each hemisphere, and by the position of the sun's shadow on the marked hemisphere sections, it is possible to read the supernal coordinates of the sun.
He also set up an astrolabe, the 'Raj Yantra', which is a map of planetary positions depicted on a 7 foot wide metal disc, to whose fundamentals and practical use, he devoted two volumes.
Jai Singh was far more accurate than Ptolemy and Ulugh Beg in measuring the precession (the motion of a spinning body in which it vibrates and causes the axis of rotation to sweep out a cone) of the equinoxes, and the abnormality of the ecliptic (the great circle representing the annual solar path; the plane of the Earth's orbit around the sun; makes an angle of about 23 degrees with the equator). However, surprisingly, he failed to take into consideration many of the important European discoveries of his time, like Copernicus's heliocentric concept, that maintained that it was the Earth that moved around the sun and not the other way round.
Jai Singh opened his observatories to the public in order to popularize astronomy, and also sponsored a scientific delegation to Portugal under the Jesuit, Padre Manuel de Figueredo. The emissaries, who set sail for Lisbon in 1728, returned in 1730 with the Portuguese King Emmanuel's envoy Xavier de Silva, Pere de la Hire(1640-1718)'s 'Tabulae Astronomicae' (pioneered at the Paris Observatory and first printed in 1687 with an improved version brought out in 1702), and some instruments, including telescopes. On experimenting with the foreign apparatus, he found it imperfect, and, while he did enhance his astronomical work with some of Hire's theories, he found several discrepancies too in Hire's tables. Ascribing these to the 'inferior diameter' of Hire's instruments, he sought the opinions in 1734, of two Frenchmen stationed in Chandernagore in Bengal, Father Claude Boudier (1686-1757) and Pons, who confirmed the inaccuracies in Hire's tables. He made plans for sending a second delegation to Europe, but died before he could do so, in 1743.
Jai Singh's astronomical enterprises, unfortunately, faded away after him. One of the reasons for this scientific disinterest can be that while the whole imperialistic edifice of 18th Century Europe, depended on improved Navigational knowledge that required the invention and building of precision Astronomical instruments, the Indian States of that same period felt no corresponding need and looked upon Astronomy as no more than a recreation. The Delhi Observatory was greatly damaged in 1764 by Jawahar Singh, the son of the Jat ruler of Bharatpur, Suraj Mal, and was only haphazardly restored in 1910 by the then Raja of Jaipur, for the 1911 royal tour of King George V. The Jaipur Observatory, which was transformed into a gun factory by Jai Singh's grandson and its astrolabe used for target practice, was however excellently repaired under the direction of Chandra Dhar Sharma Guleri in 1901. Today, Jantar Mantars are open to tourists and are well-worth a visit.