RECENT COSMOGONIES 243 



able her to sunder a steel cable more them thrice her own 

 diameter! Did I say sunder? That is the wrong word, 

 for the bond of gravitation may be strained, indeed, but 

 not broken. When the moon was hurled, as alleged, to 

 the distance of 4,000 miles from the earth and became a 

 satellite, their mutual attraction was thereby by no means 

 destroyed, but only reduced to 1-4 of what it was before, 

 equaling still the strength of an elastic steel cable 12,000 

 miles in thickness, or 1-J^ times the earth's diameter. 

 From that point on outward, Darwin assumes, by conven- 

 tion, that the momentum of the moon possessed at the in- 

 stant of severance persists undiminished forever, sus- 

 taining her in her orbit automatically ; and then he goes 

 on to explain how the gravitational attraction of the 

 ansae, or tidal protuberances of the moon, lift her further 

 <md further away by her boot straps, as it were. 



The velocity from infinity, or parabolic velocity, is 

 that which a body falling from infinity would acquire on 

 reaching the cosmic body under consideration. Thus, a 

 cannon-ball falling to the earth from infinity would ac- 

 quire, according to mathematicians, a velocity of 6.9 miles 

 a second. Conversely, in order that any object expelled 

 forcibly from the earth shall never return to it again, it 

 must depart with this same velocity of 6.9 miles a second. 

 Now, according to Darwin's premises, the moon must 

 have been flung off with just that speed, since it appears 

 she is never to return to the earth. 



The query here suggests itself, what was the nature 

 of the energy that accomplished this stupendous cast! 

 It could not have been heat, because Darwin lays the 

 cause of the earth's axial acceleration to its having cooled 

 and shrunken. Furthermore, it can be shown that as 

 much flinging energy would have been required as there 

 would be heat generated by the reverse process of the 

 fall of the moon from infinity upon the earth ; that is to 

 say, more than enough to vaporize both of these great 

 bodies completely, Comparing the moon to a projectile 

 being fired from the earth, against the latter 's retarding 

 attraction, out of a suitable cannon, at the initial velocity 



