AEROLITES. 121 



of fire-balls and shooting stars, wliicli has frequently been ob- 

 served to be opposite to that of" the Earth, ma}^ be considered 

 as conclusive arguments against the hypothesis 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 surrounded by any atmosphere, 

 must, from their nature, be wholly arbitrary. We may imag- 

 ine the reaction of the interior of a planet on its crust ten or 

 even a hundred times greater than that of our present terres- 

 • trial volcanoes ; the direction of masses projected from a satel- 

 lite 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 ori- 

 gin of meteoric stones* depends upon a number of conditions 



* Chladui states that an Italian physicist, Paolo Maria Terzago, on 

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

 ciscan monk was killed, was the first who surmised that aerolites were 

 of selenic origin. He says, in a memoir entitled Musceuvi Septalianum, 

 Manfredi Septalcs, Patricii Mediolanensis, indjistrioso labore conslruciurn 

 (Tortona, 1664, p. 44), '^Labant philosophorum meutes sub horum lapidum 

 ponderibus ; ni dicire velimus, lunam terram alteram, sine mundum esse, 

 ex cujus montibus dwisa frustra in inferior em nostrum hunc orbe^n dela 

 bantury Without any previous knowledge of this conjecture, Olbers 

 was led, in the year 1795 (after the celebrated fall at Siena on the 16th 

 of June, 1794), into an investigation of the amount of the initial tangen- 

 tial force that would be requisite to bring to the Earth masses project- 

 ed 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 w^as then so prevalent, but which has 

 since been abandoned, of the existence of active volcanoes in the Moon, 

 where 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 resistance of the air, an initial velocity of 8292 feet in the second ; 

 according to Laplace, 7862 ; to Biot, 8282 ; and to Poisson, 7595. La- 

 place states that this velocity is only five or six times as great as that of 

 a cannon ball; but Olbers has sliown "that, with such an initial veloc- 

 ity as 7500 or 8000 feet in a second, meteoric stones would arrive at the 

 surface of our earth with a velocity of only 35.000 feet (or 1-53 German 

 geogi'aphical mile). But the measured velocity of meteoric stones av- 

 erages five such miles, or upward of 114,000 feet to a second ; and, 

 consequently, the original velocity of projection from the Moon must 

 be almost 110,000 feet, and therefore fourteen times greater than La- 

 place asserted." (Olbers, in Sebum., Jahrb., 1837, p. 52-58; and in 

 Vol. I.— F 



