146 NOMOS. 



The moon of the earth ? This is a natural difficulty, 

 but > with Newton's help, it is easily 

 disposed of. There is, no doubt, an 



the sun, and amazing difference between the heat- 



the tidal ex- 



pansion ing powers of the sun and moon, and the 



causes win be whole of this difference may be allowed. 



" 1 It ma 7 be allowed that the heating powers 



sun - of the sun are 200 or even 300 times 



more powerful than those of the moon, and that the 

 earth would shrink to the dimensions of the moon if 

 the solar heat was withdrawn; and still the tidal 

 expansion dependent upon the moon will be greater 

 than that which is dependent upon the sun. This is 

 evident, for the tidal expansion is the measure, not of 

 the whole amount of the expansion, but of certain 

 fluctuations in this expansion, which fluctuations 

 must be far greater in the lunar than in the solar 

 expansion. All this may be shown in the same way 

 as that by which Newton has shown that the moon 

 must attract the tidal wave more than the sun. 

 According to the theory of universal gravitation, the 

 tides are caused, not by the whole amount of the 

 attraction of the sun and moon upon the waters, 

 but by the inequality of this attraction on different 

 sides of the earth. If the tides were due to the 

 entire amount of attraction, then the tide of the 

 sun would be much higher than that of the moon; 

 but as they are owing to certain differences of 

 attraction, the tide of the moon is the highest. And 

 this must be so. The attraction diminishes as the 

 distance increases, and therefore the attraction of the 

 sun and moon upon the earth must be greater upon 



