108 COSMOS. 



velocity. This planetary velocity* 4 , as well as the direction of 

 the orbits of fire balls and shooting stars, which has fre- 

 quently been observed to be opposite to that of the Earth, 

 may be considered as conclusive arguments against the hypo- 

 thesis that aerolites derive their origin from the so-called 

 active lunar volcanoes. Numerical views regarding a greater 

 or lesser volcanic force on a small cosmical body, not sur- 

 rounded by any atmosphere, must from their nature be wholly 

 arbitrary. We may imagine the reaction of the interior of 

 a planet on its crust ten or even a hundred times greater 

 than that of our present terrestrial volcanoes ; the direction 

 of masses projected from a satellite revolving from west to 

 east might appear retrogressive, owing to the Earth in its 

 orbit subsequently reaching that point of space at which these 

 bodies fall. If we examine the whole sphere of relations 

 which I have touched upon in this work, in order to escape 

 the charge of having made unproved assertions, we shall find 

 that the hypothesis of the selenic origin of meteoric stones f 



* The planetary velocity of translation, the movement in the orbit, 

 is in Mercury 26'4, in Venus 19*2, and in the Earth 16'4 miles in a 

 second. 



t Chladni states, that an Italian physicist, Paolo Maria Terzago, on 

 the occasion of the fall of an aerolite at Milan, in 1660, by which a 

 Franciscan monk was killed, was the first who surmised that aerolites 

 were of selenic origin. He says, in a memoir entitled Muswum Sep~ 

 talianum, Manfredi Septalce, Patricii Mediolanensis, industrioso la- 

 bore constructum. (Tortona, 1664, p. 44), " Labantphilosophorum mentes 

 sub horum lapidum ponderibus ; ni dicere velimus, lunam terrain 

 alteram, sine mundum esse, ex cujus montibus divisa frustra in infe- 

 riorem nostrum hunc orbem delabantur" Without any previous know- 

 ledge of this conjecture, Gibers was led, in the year 1795 (after the 

 celebrated fall at Siena, on the 16th of June, 1794), into an investi- 

 gation of the amount of the initial tangential force that would be 

 requisite to bring to the Earth masses projected from the Moon. This 

 ballistic problem occupied, during ten or twelve years, the attention 

 of the geometricians Laplace, Biot, Brandes, and Poisson. The 

 opinion which was then so prevalent, but which has since been aban- 

 doned, of the existence of active volcanoes in the Moon, whero air and 

 water are absent, led to a confusion in the minds of the generality of 

 persons between mathematical possibilities and physical probabilities. 

 Olbers, Brandes, and Chladni thought " that the velocity of 16 to 32 

 miles with which fire balls and shooting stars entered our atmosphere," 

 furnished a refutation to the view of their selenic origin. According 

 to Olbers, it would require to reach the Earth, setting aside the re- 



