506 On the Formation of Meteorites, and Volcanic Agency. 



probably have possessed if the lunar craters had been formed 

 by gaseous explosion. In view of this difficulty a suggestion 

 has been put forth in a recently published work*, that the 

 volcanic activity on the lunar surface has been due to expan- 

 sion attending solidification. Were this a correct interpreta- 

 tion, it would equally follow that during the freezing of 

 water, which also expands on becoming solid, eruptive 

 phenomena, accompanied by the formation of craters, would 

 certainly be occasionally observed ; but such, it need hardly 

 be stated, are unknown. It appears to us, however, that the 

 difficulty which would be disposed of by such an hypothesis 

 has never actually been presented. It cannot have been by 

 means of permanent gases alone that the volcanic changes on 

 the moon have been brought about ; and if vapours took part in 

 these operations they must have been subsequently absorbed by 

 the rocks forming the lunar surface, We have, however, thus far 

 not been driven to have recourse to Samann's theory f, accord- 

 ing to which the surface of the moon was at an earlier epoch 

 covered with water which has subsequently been absorbed. 

 We shall defer the examination of this subject to a later 

 occasion. 



All these considerations, then, have led us to the conclusion 

 that volcanic agency, resulting in the disintegration and dis- 

 tribution of rocky masses in space, is inconceivable without the 

 simultaneous action of gases or vapours, or of perhaps both. 

 From this it follows as a direct inference that the explosive 

 activity, to the existence of which meteorites bear evidence, 

 is due to the sudden expansion of gases or vapours, among 

 which hydrogen may have been a prominent agent. 



The conclusions arrived at from the careful investigation and 

 comparison of meteorites, confirm the results obtained during 

 the last few years by students of geology and astronomical 

 physics, The volcanic activity of which those mysterious 

 masses of stone and metal are evidence may be compared to 

 the violent movements on the solar surface, the more feeble 

 action of our terrestrial volcanoes, or the stupendous erup- 

 tive phenomena of which the lunar craters tell the history. 



No one who at this juncture bears in mind Kant's theory 

 of the homogeneous development of stellar masses, can fail to 

 be struck with the idea that the heavenly bodies already 

 alluded to are not the only masses which have undergone 

 these changes, but will rather incline to the opinion that 

 volcanic activity is a cosmical phenomenon in the sense that 



* Nasinyth and Carpenter, ' The Moon ' (London, 1874), p. 98. 

 t Samann, Bull. Soc. Geol. [2] xviii. 322, 



