320 OOSMIO PHIL080PHT. [pt. ii. 



condensing cloud an amount of molecular motion in excess 

 of that which it loses from moment to moment, condensation 

 ceases, and the particles of vapour begin to be dissipated. 

 The deposit of sediment at the mouth of a river is attended 

 by the loss of the molar motions which brought its con- 

 stituent particles from the upland regions which the river 

 drains ; and the hardening of the sediment into rock is a 

 change to a state of aggregation in which, along with greater 

 cohesion, the particles possess less mobility than before. In 

 like manner the hardening of an igneous rock is effected 

 by cooling, which implies the loss of internal motion. In- 

 deed the phenomena of heat and cold exhibit en masse an 

 illustration of the general principle. The progress of any 

 mass of matter from a gaseous to a liquid, and thence tc 

 a solid state, is attended by the continuous dissipation of 

 molecular motion ; while change in the contrary direction is 

 attended by a continuous absorption of such motion. With 

 molar motions the case is precisely similar. " Augment the 

 velocities of the planets, and their orbits will enlarge ; the 

 solar system will occupy a wider space. Diminish their 

 velocities, and their orbits will lessen ; the solar system will 

 contract. And in like manner we see that every sensible 

 motion on the earth's surface involves a partial disintegration 

 of the moving body from the earth, while the loss of its 

 motion is accompanied by the body's reintegration with the 

 earth." Finally, if we consider the case of organisms, we 

 find that the incorporation of food into the substance of 

 the tissues is constantly accompanied by the giving out of 

 motion in some form of organic activity, while conversely. 

 the decomposition which follows death is attended by an 

 immense absorption of molecular motion. The latter state- 

 ment is proved by the fact that the elements of which such 

 an organism as the human body is composed, have more 

 than twenty times the volume when free which they have 

 when combined; and it is further illustrated by the fact 



