94 ON COMETS. 



great and general attractive force which keeps the planets 

 in their orbits and they have actually informed us of 

 the weight of one of the planets which could not have 

 been determined with any exactness if a comet had not 

 on one occasion passed very near to it. 



(3.) The ancients believed comets to be much of the 

 same nature as meteors or shooting stars either in the 

 earth's atmosphere not far above the clouds ; or, at all 

 events, much lower than the moon or else as a species 

 of vapours or exhalations raised up from the earth by 

 the sun's heat, or by some other unknown cause ; but 

 they never for a moment dreamed of their forming part 

 and parcel of that vast system of planetary bodies cir- 

 culating about the sun, of which in fact they had hardly 

 any distinct notions. In ancient history, however, 

 several very remarkable comets stand recorded. One 

 is mentioned by the Greek philosopher Aristotle in 371 

 B.C., with a tail extending over a third part of the sky. 

 Many great comets are recorded at even more ancient 

 dates in the Chinese annals : for that strange people kept 

 an official record of all the remarkable stars, meteors, 

 and other celestial appearances, for more than a thou- 

 sand years before the Christian era, and what is stranger 

 still, that record has been handed down to us and seems 

 dependable. A great comet was seen close to the sun 

 62 years before Christ, during a total eclipse and one 

 which appeared in the year 43 B.C., soon after the 

 murder of Julius Caesar at Rome, was seen by all the 

 assembled people in full daylight. Such a thing, though 

 very uncommon, is by no means singular it has hap- 



