MATTER AND ENERGY. 47 



of the subject, but simply the fact that in the transpo- 

 sition of matter collisions render nebulous such a por- 

 tion of the general whole as may be subjected to the 

 immense shock to the nebularizing process. The 

 nebular theory is hardly mentionable unless associated 

 with that of collision. There must be a cause for 

 the nebularization of matter, as there is for the ag- 

 gregation of it into stellar masses. If the nebular 

 theory be correct, there need be no thought of a be- 

 ginning or of an end, but in the transformation of 

 matter from one state or condition to another, the 

 ponderable medium of the universe is sometimes neb- 

 ulous and as often as solid as a planet. 



THE EARTH. 



That the earth was once a diffused mass of gas is 

 not improbable; that it cooled and contracted to a 

 molten state is also plausible; and that it further 

 cooled and condensed to something like its present 

 state is demonstrable. At length a smooth envelope 

 of crystalline character was attained by agencies al- 

 ready cited; and this case inclosed a molten mass 

 within. Some part of the melted stuff still exhibits 

 itself through the craters of volcanoes. Such vents 

 for the fused mass within were once much more nu- 

 merous than at present. Lastly, the crust was bent 

 and warped by internal commotion, mountains and 

 corresponding valleys being developed by the disturb- 

 ing agencies. The globules of moisture which through 

 excessive heat were suspended as vapor, were floated 

 to mountain tops and there condensed into rain. 

 Through the force of gravitation the water " ran down 

 hill," forming rills and rivulets, and collected in pools. 

 Thus the river system was commenced. The surface 



