king and the Duke of York were each supplied with a barometer and thermometer made from his models, besides a copy of his rules for forecasting the weather by their means. Early in 1675 Moore again summoned him from Derby for the purpose of consulting him about the establishment of a private observatory at Chelsea to be placed under his direction.
A certain ‘bold and indigent Frenchman,’ calling himself the Sieur de St. Pierre, proposed at this juncture a scheme for finding the longitude at sea, and through the patronage of the Duchess of Portsmouth obtained a royal commission for its examination. Flamsteed was, by Sir Jonas Moore's interest, nominated a member, and easily showed the Frenchman's plan to be futile without a far more accurate knowledge of the places of the fixed stars, and of the moon's course among them, than was then possessed. Charles II thereupon exclaimed with vehemence that ‘he must have them anew observed, examined, and corrected for the use of his seamen.’ Flamsteed was accordingly appointed ‘astronomical observator’ by a royal warrant dated 4 March 1675, directing him ‘forthwith to apply himself with the most exact care and diligence to the rectifying the tables of the motions of the heavens, and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting the art of navigation.’ A site in Greenwich Park was chosen for the new observatory by Sir Christopher Wren, and the building was hastily run up from his design at a cost of 520l., realised by the sale of spoilt gunpowder.
Flamsteed was ordained by Bishop Gunning at Ely House at Easter 1675, and continued to observe at the Tower and afterwards at the queen's house in Greenwich Park, until 10 July 1676, when he removed to the Royal Observatory. He found it destitute of any instrument provided by the government; but Sir Jonas Moore gave him an iron sextant of seven feet radius, with two clocks by Tompion, and he brought from Derby a three-foot quadrant and two telescopes. His salary was 100l. a year, cut down by taxation to 90l., and for this pittance he was expected, not only to reform astronomy, but to instruct two boys from Christ's Hospital. His official assistant was a ‘surly, silly labourer,’ available for moving the sextant; and his large outlay in procuring skilled aid and improved instruments obliged him to take private pupils, numbering, between 1676 and 1709, about 140, many of them of the highest rank. Under these multiplied disadvantages, and in spite of continued ill-health, he achieved amazing results. The whole of the theories and tables of the heavenly bodies then in use were visibly and widely erroneous. Flamsteed undertook the herculean task of revising them single-handed. ‘My chief design,’ he wrote to Dr. Seth Ward on 31 Jan. 1680, ‘is to rectify the places of the fixed stars, and, of them, chiefly those near the ecliptic and in the moon's way’ (Baily, Flamsteed, p. 119). His first observation for the purpose was made on 19 Sept. 1676, and he had executed some twenty thousand by 1689. But they were made in the old way, by measuring intermutual distances, and gave only the relative places of the stars. He had as yet no instrument fit to determine the position of the equinox, but was compelled to take it on trust from Tycho Brahe. A small quadrant, lent to him by the Royal Society, was withdrawn after Sir Jonas Moore's death on 27 Aug. 1679, with which event, he remarks, ‘fell all my hopes of having any allowance of expenses for making such instruments as I still wanted.’ After some fruitless applications to government, he resolved to construct at his own cost a mural quadrant of fifty inches radius, which he himself set up and divided in 1683. With its aid he took the meridional altitudes of a number of stars with an estimated error of half a minute, and formed a rough working catalogue of some of the principal. But the quadrant proved too slight for stability, and the old sextant was after a time again resorted to.
In 1684 Flamsteed was presented by Lord North to the living of Burstow in Surrey, and his circumstances were further improved by his father's death in 1688. With the aid of Abraham Sharp [q. v.] he was thus enabled to undertake the construction of the mural arc with which all his most valuable work was executed. Its completion marked a great advance in the art of mathematical instrument making. The limb, firmly fixed in the meridian, was of 140°, and was divided with hitherto unapproached accuracy; the radius was of seven feet. Observations with it were begun on 12 Sept. 1689. ‘From this moment,’ Baily writes (Flamsteed, p. xxix), ‘everything which Flamsteed did … was available to some useful purpose, his preceding observations being only subsidiary, and dependent on results to be afterwards deduced from some fixed instrument of this kind.’ His first concern was to determine the latitude of the observatory, the obliquity of the ecliptic, and the position of the equinox; and the method employed for this last object, by which he ascertained absolute right ascensions through simultaneous observations of the sun and a star near both equinoxes, was original, and may be called
