22 GEOLOGY. 



main mass into a gaseous state. If the collision were a center-to- 

 center encounter, a radial dispersal of matter transverse to the line 

 of collision would follow; returning from which, the material would 

 again collide, and after a series of oscillations would gradually settle 

 down into a pulsating gaseous mass. 1 Here again the system would 

 become gaseous at the outset, and probably develop nothing of the 

 typical meteoritic kind except possibly such sporadic elements as 

 might be projected beyond the control of the system. If the collision 

 were excentric, a rotatory motion would doubtless be superposed 

 upon the radial motion, and the case would either fall under the gase- 

 ous or the orbital system, or under a combination of the two. 



(c) Dispersion by tidal disruption. — It has recently been sug- 

 gested that bodies passing close by one another, but not colliding, 

 may suffer disruption through their differential attractions aided by 

 internal elasticity, 2 on the principles developed by Roche, Maxwell, 

 and others. In this case the disrupted elements are given a rotatory 

 movement in a common direction and in the plane of the two bodies 

 initiating it. The dynamics of the system are therefore from the out- 

 set definitely of a rotatory or revolutionary kind, and the case falls 

 under the orbital or planetesimal system rather than the meteoritic 

 system. 



It appears, therefore, that neither explosion nor collision nor tidal 

 disruption is likely to give rise to a distinctively meteoritic swarm, 

 and no other definite source is known to us. Individual meteorites 

 and rotatory or revolutionary assemblages of dispersed elements, 

 as well as true gaseous nebulae, may be supposed to arise from the 

 catastrophes named, but apparently these catastrophes are not appro- 

 priate agencies for producing fragmental swarms of the distinctively 

 meteoritic type. 



The Evidence of the Meteorites Themselves. 



The origin of meteorites bears on the question whether they are 

 the essential material from which stellar systems are derived, or are 



1 A case of this kind is described by Kelvin, Popular Lectures and Addresses, I, 

 1891, p. 413. 



2 On the Possible Function of Disruptive Approach in the Formation of Meteor- 

 ites, Comets, and Nebulae, T. C. Chamberlin, Astrophys. Jour., Vol. XIV, 1900, pp. 

 17-40, and Jour. Geol., Vol. IX, 1901, p. 369. 



