DIASTROPHISM AND THE FORMATIVE PROCESSES 141 



How far would such aggregation be likely to go, as a rule? 

 There is no need to consider exceptional possibilities, for our 

 problem relates to the common average result. The attraction 

 between two molecules oppositely charged is many bilHon times 

 greater than their gravitative attraction^ and may be large compared 

 with the inertia of their relative motion. Charged molecules 

 might then serve as very efficient centers for the gathering-in of 

 molecules, as also very small particles. But an electric charge is 

 confined to the surface of a particle, which increases as the square 

 of its radius, while gravitation varies as the mass which increases 

 as the cube of the radius. And so, after a certain amount of growth, 

 the charges carried on the particles would have less attractive 

 power than the masses into which the particles had grown. But a 

 more important practical consideration Ues in the fact that electric 

 charges of like kind repel one another and thus limit the total 

 charge Hkely to be gathered on a given mass under natural condi- 

 tions; for example, any electric charges which a forty-pound 

 boHde would probably pick up naturally would lend Httle aid in 

 gathering in other forty-pound bohdes to form a forty-ton bolide. 

 There is thus an obvious limitation to the range of effective electric 

 aggregation, however efficient it may be as an originating agency. 

 A beautiful illustration at once of such effective aggregation and of 

 its limitation is presented by the formation of snow crystals from 

 vapor in the air. These form and grow with great facihty up to 

 a certain size when the temperature of moist air falls below the 

 freezing-point; but after a certain moderate growth, the limiting 

 and adverse conditions increase in relative efficiency and arrest 

 further growth; not infrequently it is reversed. 



In the case of cosmic particles probably the most effective 

 preventive of indefinite growth is the friction and collision of the 

 masses, themselves. As the particles grow into nodules of notable 

 size and mass, their cohesion is less effective relative to their moving 

 force, and they more readily go to pieces on impact. Trituration 

 and other lesser effects of moving contact would be more frequent 



*R. A. Millikan, in a personal communication, states: "The attraction of two 

 opposite electric charges is lo^' times as great as the gravitative attraction of two 

 atoms of hydrogen." 



