726 THE UNIVERSE. 



We have, therefore, no reason to dread their contact, and 

 may sleep securely. In 1770 astronomers saw a comet bar 

 the path of Jupiter's system, and envelop the planet on 

 every side, without the slightest perturbation to the course 

 either of the great star or that of its satellites. On the 

 contrary, it was the nebulous star that suffered from the 

 contact. Besides, it seems that during the passage of cer- 

 tain comets in our vicinity, their tails may have penetrated 

 into our atmosphere. 1 



However, according to Maupertuis, though there are 

 some comets so small that their 'collision with the earth 

 would only destroy a few kingdoms, without shattering its 

 mass, there are others the contact of which might be fatal 

 to every living thing on the globe. 



In his " Lettres Cosmologiques," Lambert leads us to 

 dread the most serious accidents. According to him, the 

 shock of a comet might pulverize our globe, and prove the 

 destruction of everything living on it by means of a deluge 

 of water or a general conflagration ; or comets might even 

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

 hurl us beyond the regions of Saturn, where hideous winter 

 reigns for ages together. 



of matter in the shape of ignited gas, and that this matter is similar in constitution 

 to the gaseous material of some of the nebulae. The coma was found to shine by 

 reflected light, and as, from its extreme diffusion, it cannot be supposed to contain 

 solid or liquid matter at the high temperature necessary for incandescence, it 

 seems almost certain that it reflects the light of the sun. The nucleus of meteors 

 is probably a fragment of mineral matter, of which sodium is one of the chemical 

 ingredients. Their spectra are often highly colored and continuous, like those 

 from solid matter at a white heat. TK. 



1 According to Humboldt, the tails of the comets in 1819 and 1823 must have 

 reached our atmosphere. The same thing is supposed to have happened with the 

 last great comet observed in our latitudes. 



