348 METEORS. 



philosophers was accordingly directed to this part of the 

 heavens, until, in the nineteenth century, four very small 

 planets were discovered, which have been called, from 

 their diminutive size, asteroids. Their.names are Vesta, 

 Juno, Pallas, Ceres. One of them is estimated to be only 

 eighty miles in diameter. The estimates, however, vary 

 very much. 



The most remarkable circumstance, however, which is 

 connected with these asteriods, is this. They all have 

 very nearly the same average distance from the sun, the 

 same period of revolution in their orbits they are of the 

 same density ; that is, the matter which composes themes 

 of the same weight and in the points at which each 

 of them approach the sun, called their perihelions, and in 

 those where their orbits cross the elliptic, all the asteroids 

 agree. 



These are certainly extraordinary coincidences. They 

 have given rise to the hypothesis that these four bodies 

 were originally one large planet, which by some vast con- 

 vulsion, of which we can know nothing in detail, was 

 rent asunder, separating itself into four large, and a mul- 

 titude of small fragments. These four large fragments, 

 it is supposed, continue to revolve around the sun, very 

 nearly in the place of the original revolution of the whole ; 

 each one deviating from the former track, according to 

 the impulse given it by the shock. 



But what connexion has all this, the reader will ask, 

 with meteoric stones? The theory which we are endeav- 

 oring to explain, imagines that some smaller fragments 

 from this fancied explosion, were thrown to a great dis- 

 tance from the original place of the planet, and that many 

 of them came into the vicinity of our earth, and that they 

 are now revolving about it, like satellites. While they 

 are moving in the empty space beyond the earth's at- 

 mosphere, they are invisible. They sometimes, however, 

 are supposed to dip into the atmosphere, for their orbits 

 being probably very eliptical, they may at times ap- 

 proach very near the body of the earth. When they thus 

 enter the earth's atmosphere^ the friction of the air dis- 

 engages fight and heat. The former makes these bodies 

 visible to us, and the latter, the heat, cracks off portions 

 of the revolving body, which fall to the earth. The main 



