ON GEOLOGICAL TIME. 19 



7. When we consider the moon as causing the 

 tides, and the change from high to low as depend- 

 ing on the rotation of the earth, it becomes obvious 

 that if there is resistance to the motion of the 

 water that constitutes the tides, that resistance 

 must directly affect the earth, and must react on 

 those bodies, the moon and the sun, whose at- 

 tractions cause the tides. The theory of energy 

 declares, in perfectly general terms, that as 

 there is frictional resistance, there must be loss 

 of energy somewhere. We are not now merely 

 content to say there is loss of energy by resist- 

 ance, but the modern theory must account for 

 what becomes of that energy. It is particu- 

 larly to Joule that the full establishment of the 

 true explanation as to what becomes of energy 

 that is lost in friction is due. I suppose every 

 one here present knows Joule's explanation, 

 namely, that heat is generated. The friction of 

 the waters against the bottom of the sea and 

 against one another, in rubbing, so to speak, as 

 they must to move about, to rise in one place and 

 fall in another the friction of waters especially 



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