fallen from the Atmo<!phere. 299 



referred to fire-balls, of which I have mentioned thirty-six 

 instances in the Connoissance des Terns for the year 8 and 

 the year 10. The work of M. Izam entitled Lithohgie 

 Atmospkerlqiie contains many details on this subject. 



These stones being of a species not to be found on the 

 earth, it has been concluded that they are formed in the at- 

 mosphere ; but several chemists consider this as impossible. 

 M. Delaplace has examined what would be the case if they 

 were projected from a lunar volcano ; and N. Poisson, an 

 able geometrician, professor in the Polytechnic School, has 

 given a learned memoir on this subject in the Bulletin des 

 Sciences *, published by the Philomatic Society; from \\'hich 

 it results, that if a body were projected from the moon with 

 a velocity of 7600 fpct per second, or five or six times that 

 of a cannon ball, it would reach the earth in two days and 

 a half, and its velocity when it arrived at the surface would 

 be 3 1 500 feet per second, making allowance for the resist- 

 ance of the air. 



But as the height of the atmosphere may be considered 

 as very small in comparison of the earth's semidiameter, 

 this velocity would be yearly equal to that which the same 

 body would have on entering into this atmosphere ; but the 

 air then acting upon it by the resistance, which increases in 

 a proportion much greater than tiie velocity, would soon 

 lessen the rapidity of this motion, which would become 

 i^cnsibly uniform, like that of bodies which fall into a resist- 

 ing fluid of considerable depth. 



JM. Biot, wiio was at Laigle to collect all the circum- 

 stances of this phenomenon, presented to the Institute a 

 very long and satisfactory report on this subject, which has 

 been piinted. From the circumstances which he relates, 

 it appears to me difficult not to believe that these stones 

 w ere formed at the same time as the globe of fire. The 

 number which fell was two or three thousand : they wefc 

 exceedingly hot, scorched at the surface, and almost fria- 

 ble ; but they became hard on cooling. 



M. Izam has made no mention of the stones which felf* 

 on the Jrtth of June 1794, seven leagues to the south-west 

 of Sienna in Tuscanv, and respeeiing which there is a work 

 entitled Sopra jAogvlta di sassi accaduia nctla sera de IC G'i- 

 vgno 17!»4, Dhsertazinne del P. D. Aivhrnzio Soldani in 

 Sicna 1794. Bvo. Fifty or sixty fell in the compass of a 

 mile ; they were liot and burning at the surface, like those 



■' No. 71. 

 P ,T ^^llicU 



