ment given to a ‘heliostat’ by Ramsden, mounted in President Saron's observatory in Champagne, was so accurate that Von Zach once followed Sirius with it during twelve hours (Berl. Astr. Jahrbuch, 1799, p. 115).
Ramsden published in 1777, by order of the commissioners of longitude, a ‘Description of an Engine for dividing Mathematical Instruments.’ In a preface by Maskelyne, it is stated that he received 315l. from the government by way of premium for this important invention, and 300l. for his property in it. The ‘Description’ was translated into French by Lalande in 1790. A ‘Description of an Engine for dividing Straight Lines on Mathematical Instruments’ was issued by Ramsden in 1779. On 25 March of the same year he laid before the Royal Society a ‘Description of two new Micrometers’ on the double-image principle, one by reflection, the other by refraction (Phil. Trans. lxix. 419); and on 19 Dec. 1782 a paper on ‘A New Construction of Eyeglasses,’ by which the aberrations of colour and sphericity were much diminished (ib. lxxiii. 94). Before 1789 he had constructed nearly a thousand sextants, greatly improved from Hadley's design; he made a new instrument of the theodolite; devised novel methods for illuminating the wires of transits and determining their collimation errors; invented a ‘pyrometer’ for measuring the expansion of substances through heat; a ‘dynameter’ for ascertaining telescopic powers; and was the first to apply ‘reading-off microscopes’ to circular instruments. His most famous work was a five-foot vertical circle, turned out in 1789 with admirable perfection under Piazzi's personal supervision for the Palermo observatory. Its high qualities rendered inevitable the substitution of entire circles for quadrants and sectors, a reform consistently advocated by Ramsden. From observations made with it, Piazzi constructed his great star-catalogue, and he described it in detail with illustrative plates in ‘Della Specola di Palermo’ (i. 15). A similar but larger instrument was built by Ramsden for the Dublin observatory.
A fine zenith-sector, constructed for the measurement of the British arc, was finished by his successor Berge in 1803. Placed for safety in the Tower, it perished in the fire of 1841. William Pearson [q. v.] described and figured it in his ‘Practical Astronomy’ (ii. 533–46). A theodolite four feet in diameter, carrying telescopes of three feet focus, was delivered by Ramsden in 1787 for use in General Roy's survey. It was eventually presented by George III to the Royal Society. The delay of three years in completing it caused great inconvenience (Phil. Trans. lxxx. 111), but the artist's genius disdained time restrictions (Zach, Monat. Correspondenz, vii. 251). On one occasion he attended at Buckingham House precisely, he supposed, at the time named in the royal mandate. The king remarked that he was punctual as to the day and hour, while late by a whole year.
He was elected a member of the Royal Society on 12 Jan. 1786, and of the Imperial Academy of St. Petersburg in 1794. The Copley medal was bestowed upon him in 1795 for his ‘various inventions and improvements in philosophical instruments.’ Among the first were an electrical machine, barometer, manometer, assay-balance, and level. A duplicate of his dividing-engine was said to have been introduced by President Saron into France, concealed in the pedestal of a table. He became acquainted with Von Zach in 1783; the Dukes of Marlborough and Richmond frequently entertained him; and Piazzi expressed veneration for his memory, and showed his portrait to an English traveller in 1813 (Hughes, Travels in Greece and Sicily, i. 131).
After some years of declining health, Ramsden went to Brighton to recruit, and there died on 5 Nov. 1800, aged 65. Delambre styled him ‘le plus grand de tous les artistes.’ The demand from all parts of Europe for his incomparable instruments was greater than could be satisfied by the constant labour of sixty workmen; yet they were considerably cheaper than those by other makers. His life was one of extreme frugality. He ate and slept little and studied much. His favourite scientific authors were Euler and Bouguer, and in advanced years he learned French enough to read Boileau and Molière. Most of his evenings were spent drawing plans by the kitchen fire, a cat on one side, a mug of porter and plate of bread and butter on the other, while some apprentices sat round, and he whistled or sang. After explaining a design to a workman, he would say, ‘Now, see, man, let us try to find fault with it,’ and intelligent suggestions generally led to amendments. But if a completed instrument fell short of his ideal, it was invariably rejected or destroyed, with the exclamation, ‘Bobs, man! this won't do; we must have at it again.’ In consequence of this disregard of gain, he left but a small fortune, mostly divided by will among his workmen. A portrait of him by Robert Home (d. 1836?) [q. v.], engraved by Jones in 1791, was given by Sir Everard Home to the Royal Society. The