METEORS AND AEROLITES. 283 



The hypothesis, thus powerfully advocated, has been dis- 

 placed not so much by any recent negative proofs, as by 

 the want of further and more assured evidence; and by 

 the adoption of new theories which connect the phenomena 

 of aerolites more directly with those of other meteors, and 

 associate the whole with the general conditions of the pla- 

 netary system. The lunar theory, to say the least of it, has 

 remained stationary at the point whence it started ; nor is 

 there, as far as we can see, any source of fresh knowledge 

 within our reach. Even with the powerful telescopes we 

 now possess, no proof has been obtained of present volcanic 

 activity in the Moon ; and, looking backwards to that which 

 may have existed heretofore, we must admit the need of a 

 projectile force much greater than that first presumed, to ex- 

 plain the actual mean velocity of aerolites in approaching 

 the earth. It has been calculated by Gibers (and we believe 

 not disputed) that the initial velocity at the Moon, to satisfy 

 this condition, must be twelve or fourteen times greater than 

 that assigned by Laplace and others ; a projectile force far 

 exceeding that of our own volcanoes, and which, did it really 

 exist, would not cast these masses upon the earth, but cause 

 them, as Olbers and Bessel have shown, to revolve in orbits 

 about the Sun. 



Another hypothesis, having kindred with the one just con- 

 sidered, is that which supposes these aerolites to be smaller 

 fragments of that presumed ancient planet between Mars 

 and Jupiter, the disruption of which has produced the many 

 small planets -or asteroids, whose excentric orbits cross and 

 crowd each other in this part of the heavens. But a few years 

 ago only four of such ultra-zodiacal bodies were known 

 to us. The position and peculiar orbits of these justified 

 Olbers in his bold conjecture of their fragmentary nature; 

 an opinion greatly strengthened by the later discovery of 

 numerous others in the same interplanetary space, many of 



