524 PHILOSOPHICAL TRANSACTIONS. [aNNO 1 681-2. 



of the star or head, and transmit others which make the appearance of the tail 

 or blaze. 



u4n Account of a Treatise concerning the late Comet, Published at Turin l681, 

 By l)onato Rossetti, S. T. D. Canon of Leghorn, and now Reader of Philoso- 

 phy in the University of Pisa, and Tutor in Mathematics to the Duke of 

 Savoy. Philos. Collect. N°4, p. 114. 



In this treatise is found little of observation on this comet, but only on ac- 

 count of the ingenious author Dr. Rossetti's own thoughts and theory, con- 

 cerning the various phaenomena of comets in general. He conceives then that 

 all the comets that have ever yet appeared, have been de novo generated, and 

 again dispersed in the elementary regions about the earth. And notwithstand- 

 ing all that has been alleged by other authors to prove them to be in much 

 higher regions, from their little or no parallax, he pretends to show that their 

 arguments are not sufficient either to prove that comets are above or beyond 

 the mooUj or to determine the distances of the planets, by reason that the re- 

 fractions that the rays from each of them suffer, in passing through the atmos- 

 phere, cause so great an irregularity, that tables sufficiently exact cannot be 

 made of the planets themselves, and therefore much less of the comets which 

 have not been yet brought to a theory. 



An Explication of the Comet which appeared at the end of 168O, and in the begin- 

 ning of 168I ; with a Table ivhich shows when it began to appear, and when it 

 should cease or disappear, together with the daily Motion of it, as to Longitude 

 and Latitude. Dijon, Jan. 8, 168I, on the Observations of Dr. Anthelme, 

 Carthusian of Dijon. Philos. Collect. N°4, p. II6. 



The contents of this tract were to show a specimen of predicting the future 

 course of the comet, from some of the first observations of it, which has been 

 attempted by several, and upon very different hypotheses. The hypothesis on 

 which the author founded his calculation, is, that comets are bodies as old as the 

 creation, and have motions as regular as the planets ; and that the reason why 

 they are but seldom seen is, that they move in vast orbs very eccentrical to the 

 earth, and are only visible in that part of the orb that approaches the earthy 

 which has so little curvature that it may be accounted almost a straight line, as 

 Kepler and some other eminent astronomers have supposed. That the bodies 

 of them are transparent, and transmit the sun's beams, which makes the blaze 

 or tail, which he supposes always opposite to the sun. He conceives them to 

 have no significancy as to mutations on the earth, as of war, sickness, famine, 

 death of great men, or the like. 



