Nipher — Primitive Conditions in the Solar Nebula. 117 



reached from a discussion of underground temperatures as 

 related to the age of the earth, and its past history. 



It seems certain that the material composing our earth 

 must have been solid when the moon separated from the 

 earth, and that the outer parts of the sun must have been 

 solid when Mercury separated from the parent mass. In its 

 subsequent history, the sun has fused and vaporized. Its 

 condition now is precisely what might be expected from the 

 teachings of the equations of the present paper. The sun is, 

 certainly, mainly gaseous. Its outer visible limit, is the clouds 

 formed of liquid drops, which occupy the external layers 

 where the temperature is comparatively low, and where some 

 of the material is not gaseous. 



The temperatures which will be attained in a condensing 

 swarm of meteorites will evidently be subject to considerable 

 variations. If the masses are uniformly distributed in a 

 spherical volume, the acceleration will approach zero at the 

 central parts, and will increase outwardly along a radius. If 

 it happen that a central core of solid matter has been estab- 

 lished, then external to this core, the acceleration will be com- 

 posed of two terms. The value of one term varies inversely 

 as the square of the distance from the core center, and that of 

 the other, due to the effect of the swarm external to the core, 

 increases directly with the radius. It may therefore happen 

 that the acceleration will be a minimum at some surface 

 within the meteoric swarm, and external to the core. If the 

 whole mass is in rotation around an axis, it is evident that such 

 a distribution of matter would result in the formation of an 

 equatorial ring. The masses external to the position of min- 

 imum acceleration would gradually gravitate inward towards 

 the position of minimum acceleration, and those within would 

 gradually separate from it. 



In determining the resulting or maximum temperature due 

 to the ao-gregation of such masses into planets, there is much 

 wider limits for conjecture, than in the case of a gaseous 

 nebula. The variation in average density throughout the 

 swarm of meteorites will depend upon the size and density 

 of individual masses. The energy may be so gradually dissi- 



