MEMOIR ON METEORITES. 305 



of attraction between the earth and moon, and already having 

 an orbital velocity, may become a satellite of the earth with a 

 modified orbit. 



The important question then for consideration is the force 

 requisite to produce this velocity. The force exercised in 

 terrestrial volcanoes varies. According to Dr. Peters, who 

 made observations on iEtna, the velocity of some of the stones 

 was 1,250 feet a second, and observations made on the peak 

 of Teneriffe gave 3,000 feet a second. Assuming, however, 

 the former velocity to be the maximum of terrestrial volcanic 

 effects, the velocity with which the bodies started (stones with 

 a specific gravity of about 3.00) must have exceeded 2,000 feet a 

 second to permit of an observed velocity of 1,250 feet through 

 the denser portions of our atmosphere. 



Doubtless the projectile force of lunar volcanoes far exceeds 

 that of the terrestrial; and this we infer from the enormous 

 craters of elevation to be seen upon its surface, and their great 

 elevation above the general surface of the moon, with their 

 borders thousands of feet above their center; all of which 

 point to the immense internal force required to elevate the 

 melted lava that must have at one time poured from their 

 sides. I know that Prof. Dana, in a learned paper on the sub- 

 ject of lunar volcanoes, argues that the great breadth of the 

 craters is no evidence of great projectile force, the pits being 

 regarded as boiling craters, where force for lofty projection 

 could not accumulate. Although his hypothesis is ingeniously 

 sustained, still, until stronger proof is urged, we are justified, 

 I think, in assuming the contrary to be true, for we must not 

 measure the convulsive throes of nature at all periods by what 

 our limited experience has enabled us to witness. 



As regards the existence of volcanic action in the moon, 

 without air or water, I have nothing at present to do, particu- 

 larly as those who have studied volcanic action concede that 

 neither of these agents is absolutely required to produce it. 

 Moreover, the surface of the moon is the strongest evidence we 

 have in favor of its occurring under those circumstances. 



But it may be very reasonably asked, Why consider the 

 moon the source of these fragmentary masses called meteor- 

 ites ? May not smaller bodies, either planets or satellites, as 

 they pass by the earth and through our atmosphere, have 



