IIQ RESEARCHES CONCERNING THE PERIODICAL 



meteoric stones were the same wherever found, and different from any known 

 terrestrial product. The latter work showed that shooting stars, whatever 

 miffht be the character of their chemical constituents, bore a close resemblance 

 to the fire-balls in their geometrical relations, and had a velocity and altitude 

 as great, if not greater, than those of the fire-balls whose paths had been deter^ 

 mined. Howard's researches set aside, at once, the theory of the atmospheric 

 or volcanic origin of the fire-balls, since, on such grounds, it was impossible to 

 account for their chemical constituents. Accordingly, Laplace," in a letter to 

 Zach, announces his theory of the selenitic origin of the fire-balls, and espe- 

 cially of the shower of aerolites at Sienna. He had found, by computation, 

 that a projectile force of six times that of gunpowder, in a lunar volcano, w^ould 

 suffice to throw these masses beyond the sphere of the moon's activity, and 

 make them satellites of the earth. The aerolites might then be the products 

 of the lunar volcanoes sent forth in such a direction, and w^th such a velocity 

 as to have their perigee within the earth's atmosphere. This view of the sub- 

 ject was maintained to the last by Laplace, and is repeated at length in his 

 Systeme du Monde, published in 1824. This theory would account for the 

 similarity of their chemical constituents, and would throw new light on the 

 subjects of the constituents of the lunar volcanoes. 



Olbers, in 1803, in the February number of the M. C, again brings forward 

 his theory of their lunar origin, suggested, but not made prominent, in 1795, 

 and gives a statement of the projectile velocity required at the moon's surface, 

 namely, about 7780 Paris feet per second, in order that these bodies should 

 reach the earth. Our cannon balls have a velocity of 1800 to 2000 Paris feet 

 per second, as stated in the Memoires de I'Academie, &c., of Paris, for 1769, 

 p. 247, et seq. The moon is known to be highly volcanic, and to have little 

 or no atmosphere, hence the plausibility of this supposition of the requisite 

 volcanic force being about four or five times that of gunpowder. There was a 

 conclusion, however, from the observations of Brandes and Benzenburg, in 

 1798, namely, that one of the meteors observed in common actually moved 

 upwards from the direction of the earth's surface, which could not be explained 

 either by the theory of their selenitic or cosmical origin. This circumstance, 

 and the slowness of the motion of some spent fire-balls, induced Chladni to 



'^ Monatliche Correspondenz, September, 1802. 



