34 GEOLOGY. 



Hypotheses of disruption and dispersion. — Any supposed explosion 

 from an internal source is unsatisfactory because it is difficult to assign 

 a sufficient and probable cause for an explosion capable of imparting 

 a velocity of several miles per second, which would probably be 

 required to disperse the fragments beyond the control of the system 

 to which the body belonged, and because, if such sufficient explosion 

 were realized, it must apparently wreck many of the peculiar meteoritic 

 structures. 



Collision with some other mass at a high velocity might be suffi- 

 cient to disrupt the body and to drive its fragments away with the 

 requisite velocity; but the imminent danger of liquefaction by the 

 inevitable heat of the impact, or of extreme pulverization of the fragile 

 material, raises doubt as to the adaptability of collision to the case of 

 some of the stony meteorites of large size, and of the hydrocarbon 

 meteorites, while it might answer well enough for minute meteorites >. 

 The relative rarity of collision also suggests a secondary place for it as 

 an agency. 



It has recently been suggested x that disruption by differential at- 

 traction might satisfy the requirements of the case, with perhaps some 

 doubt as to adequate frequency. According to principles established 

 by Roche, Maxwell and others, a small body passing within a certain 

 distance (the Roche limit) of a larger dense body will be torn into 

 fragments by differential attraction. The size of this sphere of dis- 

 ruption depends on the densities, cohesion, internal elasticities, and 

 other factors of the two bodies. For incompressible fluids of the same 

 density, Roche gives the limit of disruption as 2.44 times the radius 

 of the large body. In most such bodies, internal elasticity probably 

 exceeds cohesion and the sphere of disruption would be larger than this. 

 The moon would probably expand with some violence if its gravity 

 were suddenly removed by differential attraction. Fragmentation in 

 this way would therefore be several times more probable than an 

 actual collision. The fragmentation in this case is not minute nor 

 violent. 



A small body passing near a much larger body is liable to be thrown 

 from its previous orbit into quite a new one. This has apparently 

 happened to several comets through the influence of the planet Jupiter. 



1 Chamberlin, On the Possible Function of Disruptive Approach in the Forma- 

 tion of Meteorites, Comets, and Nebulae. Loc. cit. 



