MOVEMENTS AND DEFORMATIONS OF THE EARTH'S BODY. 557 



which, such as heat, are the products of the condensational forces, and 

 are gradually being dissipated, permitting further condensation. Where 

 the process may ultimately end, we dare not attempt to say. On the 

 other hand, we are not compelled to accept assigned limits that seem 

 to be inconsistent with the phenomena which the earth actually presents. 



2. The resisting agencies. 



Heat. — The most famihar of the active agencies that resist conden- 

 sation is heat. Upon this the existing volume of the earth is immediately 

 dependent, in some large part at least. As this heat is dissipated, the 

 earth shrinks. This shrinkage increases the force of gravity, and hence 

 the internal pressure increases, and, if further compression takes place 

 as the result of this increased pressure, additional heat is developed, 

 which checks further condensation until it is dissipated. It is this kind 

 of creative and self-checking action that determines the volume of great 

 gaseous bodies like the sun. Though their matter is far from its ulti- 

 mate density, and their self-gravity is enormous, they condense slowly, 

 because, with every stage of condensation, heat is generated which 

 antagonizes gravity and checks condensation, until at least a part of 

 the heat is radiated away. As the force of gravity increases with every 

 stage of condensation, the heat developed to hold it in check must 

 increase, and hence the famous law of Lane, that a gaseous bodj^ like 

 the sun grows hotter as it condenses. This law holds good while the 

 body remains in a gaseous state in which the maintenance of the volume 

 is essentially dependent on heat. When a body becomes liquid or solid, 

 its volume is dependent in part on forms of resistance other than heat, 

 and the force of the law is abated, though the principle still holds good. 

 In small solids, the principle has little application, since the force of 

 self-gravity is slight compared to the resisting forces, and very little 

 new heat is generated as the body loses that which it has; but in large 

 bodies, like the earth, where the condensational forces are enormous 

 and the internal temperature is very high, it is not improbable that the 

 heat generated at every stage of condensation is relatively large. It 

 has been inferred by some students of the phenomena that the condi- 

 tions in the interior of the earth are essentially those of gaseous matter, 

 so far as molecular relations are concerned, because the temperatures 

 are thought to be above the critical temperatures of the substances 

 composing it. If this be true, the new heat generated with each stage 



