C. Lloyd Morgan — Physiography. 247 



gently undulating form, and to extend in breadth those valleys 

 which rivers are always tending to extend in depth. On those 

 rocks, however, which are of a harder nature, rain has less absolute 

 power, but even here it renders the scenery less rugged ; less 

 sublime perhaps, but more beautiful. 



And how comes this rain ? We know that it falls from the 

 clouds. We know too that these clouds are formed when the air 

 above is cooled so much that it can no longer hold in solution all 

 the vapour of water which it has borne in an invisible form from 

 afar. The rain, therefore, comes from the vapour of water existing 

 in the wind. And how comes it to exist in the wind ? It is ob- 

 tained from the Atlantic Ocean. Thither then we must travel in 

 thought and try and picture to ourselves what takes place when the 

 visible liquid water is converted into the invisible gaseous vapour 

 of water. Now it is quite evident that some force is overcome^ — 

 some binding force which drew the particles of water closely together. 

 This force is cohesion. It may be likened to a strong man who 

 holds the watery particles in bondage, not indeed so severe as that 

 of the terrible ice-king of the Arctic and Antarctic regions, for they 

 are allowed free motion among each other, and are not locked in the 

 solid state, but still bondage chaining them down to the limits of the 

 ocean. This strong man will not loose his grip until he be conquered 

 by a stronger than he ; and on the Atlantic he meets with that 

 stronger man whom we call heat. 



Sun-heat sets free the particles of water from the bondage of 

 cohesion, and allows them to escape into the air. But the mastery 

 is not gained without an effort, and the value of this effort has been 

 calculated. To emancipate nine pounds weight of water particles, 

 an amount of energy has to be expended, equal to that of lifting a 

 ton to the top of a precipice 2900 feet high.^ But just as, when two 

 wrestlers struggle together, neither can master the other without a 

 true waste of his substance taking place, a waste that has ere long 

 to be made good by the absorption of a certain amount of mutton or 

 beef, so too on the Atlantic, during the struggle between cohesion 

 and heat, a certain amount of the latter is consumed and disappears. 

 The amount of heat so expended has also been calculated. In 

 setting free nine pounds of water particles an amount of heat 

 disappears sufficient to fuse 45 lbs. of cast iron.^ 



To take leave of metaphor, this amount of heat is expended in 

 overcoming cohesion and tearing asunder the particles of water. 

 The vapour particles thus formed, kept separate from each other by 

 heat, are carried by the wind to our shores ; there the air in which 

 they float is cooled ; the heat is now insufficient to overcome the 

 force of cohesion, and the water particles, no longer held apart, 

 clash together, and as they do so they generate by the shock as 

 much heat as was expended before in tearing them asunder. All 

 the heat which disappeared — was rendered latent or hidden — when 

 the vapour of water was raised from the Atlantic, is set free or 

 rendered sensible when condensation takes place. For every nine 

 1 These are two different ways of stating the same fact. 



