THE ORIGIN OF THE EARTH. 17 



of primitive chaos in which movements in all directions, with veloci- 

 ties varying greatly, but averaging twenty odd miles per second, pre- 

 vail. The critical feature is the prodigious kinetic energy which so 

 high an average velocity involves. 



Xow the only effective known force which might draw these flying 

 meteorites together into swarms and keep them together is their mutual 

 gravitation. Electric and magnetic attractions might do a certain 

 auxiliary work imder special conditions; but as these attractions are 

 accompanied by neutralizing electric and magnetic repulsions, the 

 differences between them may probably be neglected. 1 We must, 

 therefore, inquire how the controlling power of gravity compares with 

 the amoimt of kinetic energy that must be overcome. 



The mutual gravitation of small bodies is extremely feeble. For 

 example, Moult on has computed that if two spheres having specific 

 gravities of 10 and diameters of 10 feet, and hence each weighing 164 

 tons, be placed 100 feet apart and be wholly unaffected by any other 

 force than their mutual attractions, practically half a day (11.66 horns ) 

 will be required for them to draw themselves together, when each 

 has to go only -45 feet. Their mean velocity is therefore less than 

 four feet per hour, a scarcely perceptible motion. If they were separated 

 to an infinite distance and allowed to fall together, and thus to develop 

 the highest possible velocity which their mutual attraction could pro- 

 duce, it would not exceed .012 feet per second (Moult on). It is obvi- 

 ous, therefore, that if the supposed primitive meteorites moved at the 

 assigned velocities, or at velocities even remotely approaching them, 

 they would be quite beyond the gravitative control of one another 

 individually. Such meteorites, moving in opposite or transverse 

 directions, would pass by one another without appreciably deviating 

 from their courses, unless they chanced to collide. In that case they 

 would probably be shattered and dispersed, because on the average 

 they would strike at velocities many times as great as the projectiles 

 from the best modern guns. If they remained unbroken, they would, 

 if perfectly elastic bodies, exchange velocities and directions, or, if 

 perfectly inelastic bodies, would combine their momenta, unless they 



1 We are here speaking of the ordinary phenomena of electrical and magnetic 

 attraction and repulsion, as commonly understood; not of those newer and pro- 

 founder interpretations which assign inertia and other phenomena, including even 

 gravitation itself, to electromagnetic agency; much less the radical views involved 

 in the electromagnetic theory of matter, 



