VOL. I.J PHILOSOPHICAL TRANSACTIONS. Q 



the comet's motion, with mine ; and particularly at that of the tables. 

 I have, with the same method by which I find the motion of this comet, 

 easily found the principle of that author's Ephemerides, which he then 

 thought not fit to declare; and it is this, that this comet moves about the 

 Great Dog, in so large a circle, that that portion, which is described, is ex- 

 ceedingly small in respect of the whole circumference of it, and hardly dis- 

 tinguishable by us from a straight line. 



Concerning the new comet you mention, I saw it on the 1 1 th of Februar)', 

 about the 24th degree of Aries, with a northern latitude of 24° 40'. The cloudy 

 weather h'as not )^t pennitted me to see it in Andromeda, as others affirm to 

 have done. 



'^ 

 Extract of a Letter, written from Paris, containing some Reflections on 

 part of the preceding Letter. By M. AuzouT. N° 2, p. IS. 



As to the h}^othesis of Geov. Dominic Cassini, touching the motion of the 

 comet about the Great Dog in a circle, whose centre is in a straight line drawn 

 from the earth through the said star, I believe it will shortly be published iiv 

 print, as a thought that occurred to me in discoursing with one of my friends, 

 who maintained that it turned about a centre, because its perigee had been over 

 against the Great Dog, as I had noted in my Ephemerides. This particular I 

 long since declared to many of my acquaintance. I have added an observation^ 

 which I find that Signior Cassini has not made, viz. that there w^as ground to 

 think, that the comet of l652 was t^e same with the present, seeing that, 

 besides the parity of the swiftness of its motion, the perigee of it was also 

 over against the Great Dog. But, to state what grounds I had for these 

 thoughts, I said, that if they were true, the comet must needs accomplish its 

 revolution from ten to twelve years, or thereabouts. But, seeing it appears not 

 by history that a comet has been seen at those determinate distances of time, 



had pronounced was impossible to be solved. In l663 he was appointed inspector-general of the for- 

 tifications of the castle of Urbino, and superintendant of tlie rivers in the ecclesiastical state. His 

 astronomical pursuits, however, were still continued with the greatest diligence, and many important 

 discoveries were the reward of his industry. In 1 666 he printed at Rome a collection of astronomical 

 pieces, and among others a Theory of Jupiter's Satellites. Lewis XIV. of France desired leave of the 

 pope for Cassini to come to Paris, which was granted in 1669 ; but the time of his stay was Iknited 

 to six years. At the expiration of the term he was commanded to return ; and, on his refusal, his 

 places were taken from him. Cassini was the first professor of the royal observatory at Paris, which 

 was finished in 1670. Here he made numerous observations, and in l6Si he discovered four satel- 

 lites of Saturn. In 1695 he went to Italy to examine the meridian line which he liad settled in 16'55. 

 In 1700 he continued, through France, that meridian line which had been begun by Picard. Hq 

 died in 1712, in the 87th year of his age. 



VOL. I. B 



