MATTER AND ENERGY. 51 



as a nebulous mass approximates, a solid heat is, as it 

 were, squeezed out, or set free to become dissipated 

 in space,*and in going from one atom of matter to 

 another there is no call for a medium of transmission 

 other than what incidental molecules of matter may 

 furnish. In other words there is no apparent necessity 

 for an ethereal medium. 



SOLAR HEAT. 



The internal heat of the earth is no longer com- 

 petent to warm its crust sufficiently for biogenic 

 purposes. While in a nebulous state there was heat 

 in abundance, but as the gaseous substance became 

 condensed the heat in its molecules was driven out 

 and radiated into space. To counterbalance the loss, 

 an atmosphere was evolved from the environment of 

 ethereal matter. Oxygen and nitrogen held such 

 affinities for one another that air became an envelope 

 for the new-born earth. This had so many inter- 

 mixtures that it was not " pure " and respirable, but 

 time acted as a clarifier. It was thin and tenuous at 

 its outer boundaries, but denser near the earth. This 

 atmospherical envelope renders organic life possible, 

 and serves as a medium for floating clouds. Birds 

 sustain themselves in flight through the density of the 

 agent. Its pressure upon the earth is fifteen pounds to 

 the square inch at the sea level, but much more rare- 

 fied at the altitude of the highest mountains. The 

 air is, an important agency in the evolution of mundane 

 affairs. While the elastic and vibratile body trans- 

 mits sound and light with seeming facility, yet it 

 offers more or less resistance to the passage of solar 

 rays. Fortunately this friction becomes a source of 

 heat, as in a revolving axle or in any other familiar 



