758 THE UNIVERSE. 



the most serious accidents. According to him, the shock 

 of a comet might pulverize our globe, and prove the de- 

 struction of everything living on it by means of a deluge 

 of water or a general conflagration ; or comets might even 

 carry ofi" our moon by sweeping it away in their orbit, or 

 hurl us beyond the regions of Saturn, where hideous 

 winter reigns for ages together. 



But even supposing that comets are not so marvellously 

 light as to allow of a man carrying them off upon his 

 shoulders without being as strong as Atlas, and if too 

 their shock is far from being so formidable as Bufi^on 

 supposed; yet certainly these bodies are too imperfectly 

 known for us to lay down general rules about them. 

 M. Guillemin, in his remarkable woi-k on the heavens, 

 speaks as follows: "If there be comets the nebulosity of 

 which is quite gaseous, and so transparent that small stars 

 can be seen through their substance, there are others the 

 nucleus of which is without doubt very dense, as their 

 light was bright enough to be perceptible in full day, even 

 in the vicinity of the sun." 



The mass of Donati's comet has been estimated at 

 about the seven-hundredth of that of the earth. "That is 

 to say," says M. Faye, "the same weight as a sea of 16,000 

 square leagues surface, and 330 feet in depth. It must 

 therefore be admitted that such a mass, impelled with 

 great speed, might produce sensible effects by coming in 

 contact with the earth." 



Is it not possible, in cases where the tail of a comet 

 is formed of atoms Avidely scattered, that the brilliancy 

 of their nucleus may just be the result of incandescence? 

 and then, even supposing there was nothing to fear from 

 the shock, would not the approach of such a furnace be 

 enough to make us dread being burned up? 



