EVOLUTION AND DISSOLUTION 



ing out of the account the motions, both molar 

 and molecular, which they exhibit, and which 

 constitute an equally important part of the en- 

 tire process. This defect we must now endeav- 

 our to remedy. 



A brief reconsideration of the examples al- 

 ready cited will show us that universally the con- 

 centration of matter is accompanied by a dissi- 

 pation of motion, while conversely the diffusion 

 of matter is attended by an absorption of mo- 

 tion. The condensation of aqueous vapour into 

 a cloud is effected whenever it loses by radiation 

 a greater quantity of that kind of molecular mo- 

 tion known as heat than it is receiving from the 

 sun and the earth ; and when the loss of motion 

 is still more considerable, there occurs a further 

 condensation of the aqueous vapour into liquid 

 rain. Conversely, when solar radiance, direct or 

 reflected, begins to impart to the 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 constitu- 

 ent 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 par- 

 ticles possess less mobility than before. In like 



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