326 PHILOSOPHICAL TRANSACTIONS. [aNNO I669. 



you please. Then looking through the sight A, and holding the pen I in your 

 hand, move the head of the pin P up and down the outlines of the object, and 

 the point I will describe, on the paper OO O O, the shape of the object so traced. 



An Observation of Saturn , made at Paris. By M. Huygens* and 

 M. PicARD.f iV" 45, p. 900. 



On the J 7th of August, 1668, at ll-i- hr. at night, these observers, with a 

 telescope of 21 feet, saw the planet Saturn, as represented fig. 2, pi. 9, the 



* Christian Huygens, a celebrated Dutch astronomer and mathematician, was born at the Hague, 

 of a noble family, in I629. When very young he discovered an extraordinary genius for the sci- 

 ences, and soon made a rapid progress in the mathematics, under the celebrated Schooten, professor 

 at Leyden, As early as l651 he gave a good specimen of his abilities in a book entitled Theoremata 

 de Quadratura Hyperbolae, Ellipsis, et Circuli, ex dato portionum gravitatis centro. In l658 he 

 published his Horologium Oscillatorium, sive de Motu Pendulorum; containing great improvements 

 in horology, and rendering all the vibrations of a pendulum equal, by means of the cycloid. He also 

 proposed and contrived clocks for finding the longitude, and gave instructions for the use and ma- 

 nagement of them. In l659 came out his Systema Saturninum, explaining his discovery of the ring 

 of Saturn, and that of one of his satellites, which he was enabled to discover by the great perfection 

 he had given to telescopes. He wrote divers otlier works, exhibiting several ingenious inventions j 

 such as, improvements in the air-pump, the art of polishing telescopic glasses, the laws of the colli- 

 sion of elastic bodies, concerning the honour of which discovery he had a dispute with Dr. Wallis 

 and Dr. Wren, who had both made the same discovery about that time. In 1661 he visited Eng- 

 land, where he became a Fellow of the Royal Society. He made several journeys into France, and 

 at length, settled entirely in that country, with a pension from the minister Colbert, and was admitted 

 a member of the Academy of Sciences. There he resided from 1666 to 168I, when through ill 

 health he retired into his own country, where he died in l695, in the 67th year of his age, while 

 his Cosmotheoros, or Treatise concerning the Plurality of Worlds, was printing. In 1703 appeared 

 his Opuscula Posthuma, in 1 vol. 4to. But most of his works are now found in two collections, 

 each of 2 vols, in 4to. viz. the Opera Varia in iZS-i, and the Opera Reliqua in 1728. 



Huygens, like most true philosophers, loved retirement, and a quiet contemplative life; but he 

 was quite free from that melancholy disposition which is often contracted in solitude. He was pos- 

 sessed of a fine genius j endued with great application j and manifested one of the purest tastes in ma- 

 thematics of any man since the days of Archimedes. 



+ John Picard, a skilful astronomer and mathematician of France, was prior of Rille in Anjou. 

 Coming to Paris, his talents and skill in those sciences secured him a favourable reception there, and 

 he was admitted of the Academy of Sciences in I666, in the capacity of astronomer j and the same 

 year,'with M. Auzout, he published a new micrometer. In 1671 he was sent, by order of tlie king, 

 to the castle of Uraniburg, built by Tycho Brahe, in Denmark, to make astronomical observations 

 there} from whence, on his return, he brought the originals of those made by Tycho, which are tlie 

 more valuable as they differ in several places from the printed observations, and contain a book more 

 than had been published. Picard made several other important discoveries in astronomy; he was one 

 of the first who applied the telescope to astronomical quadrants; he first instituted the work called 

 Connoissance des Temps, which he conducted from l679 to l683 inclusively; he first observed the 

 light in the vacuum of the barometer, or the mercurial phosphorus; he also first of any measured 



