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HISTORY OP PHYSICAL ASTRONOMY.

In another part of the same work the author states that the Societyhave made “ observations of the fixed stars for the perfecting of astro-nomy by the help of telescopes.”* In an account of their opticallabours he asserts that they have constructed “ several excellent tele-scopes of divers lengths of six, twelve, twenty-eight, thirty-six, and sixtyfeet long, with a convenient apparatus for the managing of them; andseveral contrivances in them for measuring the diameters and parts of theplanets, and for finding the true position and distances of the sun, fixedstars, and satellites.”\

In an account of the inventions of Wren (afterwards Sir Chris-topher ), one of the Fellows of the Society, Sprat makes the followingstatement:—“ He has made two telescopes to open with a joynte like asector, by which observers may infallibly take a distance to half minutes,and find no difference in the same observation reiterated severaltimes, nor can any warping or luxation of the instrument hinder the truthof it.”I

This seems to be the same instrument as the one mentioned by Hookein his “ Animadversions upon the Machina Celestis of Hevelius, ” whereinhe states—in reply to an objection made by Hevelius that telescopicsights had never been applied to large instruments—that he had then byhim an instrument of Sir Christopher Wren ’s invention, furnished withtwo perspective sights of six feet long each, which he made use of for ex-amining the motions of the comet of 1665 §.

It appears that as early as the year 1665, Hooke wrote a letter toHevelius strongly recommending him to employ telescopic sights in pre-ference to the ordinary pinnules ||. At the meeting of the Royal Society held on the 4th of November, 1 667, there was read a letter from Heve-lius , dated October 21 of the same year, in which he expressed a desireof having one of the longest telescopes made in England pro-vided for him, and of being gratified with a full description, formerlypromised him by Mr. Hooke, of the way of applying telescopical sightsto sextants.

It appears from the foregoing statements that at least as early as theyear 1665 Wren and Hooke, tv’o of the most distinguished philosophersof the age, had employed telescopic sights in observing the celestialbodies. The earliest observations made by the use of the telescope inthis way, of which the details have been actually published, are those ofthe French astronomer Picard. In the Histoire Celeste of Lemonnierthere is an account of observations of the meridional altitude of the sun,made by Picard in the garden of the Royal Library of Paris , with aquadrant of nine feet seven inches, and a sextant of six feet, both fur-nished with telescopes. The earliest of these observations is datedOctober 2, 1667**. In his treatise on the “Measure of the Earth ” thesame admirable astronomer has described the different modes of verifica-tion to be employed in using instruments fitted with telescopic sights ff.

* Sprat’s Hist. Roy. Soc., p. 241. f Ibid., p. 250. + Ibid., p. 314.

§ “ Animadversions on the first part of the Machina Celestis,” p. 42. London , 4to,1674.

]| Hevelius in the same year replied to Hooke in a letter addressed to the RoyalSociety , for the contents of which see Hooke’s Animadversions, kc., p. 5.

<f[ Birch, History of the Royal Society , vol. ii. p. 208,

** Histoire Celeste, p. 11.

++ See also Anc. Mem. Acad, des Sciences, tome vii., p. 133.