198 OUTLINES OF NATURAL PHILOSOPHY. 



and in 1 106, in the reign of HENRY I. At all these 

 periods, appearances of a great and terrible Co- 

 met are recorded, but no such observations was 

 made as can ascertain their identity completely. 

 Synopsis Astronomic Cometicce^ subjoined to HAL- 

 ILEY'S Astronomical Tables. 



206. The Comet of 1680, mentioned above, 

 is remarkable for having approached nearer to 

 the Sun than any other that is known. At its. 

 perihelion, its distance from the Sun was only 

 -i-th part of the Earth's. It descended to the 



loo A 



Sun with great velocity, and almost perpendi- 

 cularly, and ascended in the same manner, re- 

 maining in sight for four months. 



When this Comet was in the perihelion, the diame- 

 ter of the Sun must have subtended an angle of 

 more than 100 degrees. See many interesting 

 particulars with respect to it, Princip. torn. ui r 

 prop. 41. at the end. 



The phenomena of the tails of Comets, shew the ce- 

 lestial spaces to be void of resistance. 



Some Comets have come very near the Earth. A 

 Comet in 14?2 is said by REGIOMONTANUS to 

 have moved over an arch of 120 degrees in one 

 day , and another in 1 760 moved over an arch of 

 4?1 degrees in the same space of time. As neither 

 pf them could probably have described in its orbit 



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