

8G1KNCK AND MAN. 601 



the ocean from which it c;irne. Up to the point where 

 condensation begins, an amount of heat exactly equivalent 

 to the molecular work of vaporization and the mechanical 

 work of lifting the vapor to the mountain -tops has disap- 

 peared from the universe. What is the gain corresponding 

 to this loss? It will seem when mentioned to be expressed 

 in a foreign currency. The loss is a loss of heat; the gain 

 is a gain of distance, both as regards masses and molecules 

 Water which was formerly at the sea-level has been lifted 

 to a position from which it can fall; molecules which have 

 been locked together as a liquid are now separate as vapor 

 which can recompense. After condensation gravity comes 

 into effectual play, pulling the showers down upon the 

 hills, and the rivers thus created through their gorges to 

 the sea. Every raindrop which smites the mountain pro- 

 duces its definite amount of heat; every river in its course 

 develops heat by the clash of its cataracts and the friction 

 of its bed. In the act of condensation, moreover, the 

 molecular work of vaporization is accurately reversed. 

 Compare, then, the primitive loss of solar warmth with 

 the heat generated by the condensation of the vapor, and 

 by the subsequent fall of the water from cloud to sea. 

 They are mathematically equal to each other. No particle 

 of vapor was formed and lifted without being paid for in 

 the currency of solar heat; no particle returns as water to 

 the sea without the exact quantitative restitution of that 

 heat. There is nothing gratuitous in physical nature, no 

 expenditure without equivalent gain, no gain without 

 equivalent expenditure. With inexorable constancy the 

 one accompanies the other, leaving no nook or crevice 

 between them for spontaneity to mingle with the pure and 

 necessary play of natural force. Has this u_mf prmitj, v oj 

 nature ever been broken? The reply is: "Not to the 

 ToTowledge of science/' 



What has been here stated regarding heat and gravity 

 applies to the whole of inorganic nature. Let us take an 

 illustration from chemistry. The metal zinc may he burned 

 in oxygen, a perfectly definite amount of heat being pro- 

 duced by the combustion of a given weight of the metal. 

 But zinc may also be burned in a liquid which contains a 

 supply of oxygen in water, for example. It does not in 

 this case produce flame or fire, but it does produce heat 

 which is capable of accurate mea.snrement. But the heat 



