NOMOS. 147 



the side which is nearest the sun and moon, than upon 

 the side which is opposite to this. The difference of 

 attraction may also be measured by the proportion 

 which the diameter of the earth bears to the entire 

 distance. Now the distance of the sun from the earth 

 is 12000 diameters of the earth, and consequently 

 the difference of attraction on the two sides of the 

 earth is the 12000th part of the entire amount of at- 

 traction; but the distance of the moon from the earth 

 is only 30 diameters of the earth, and consequently 

 the difference of lunar attraction on the two sides of 

 the earth is as great as the 30th part of the whole 

 amount of attraction. It is no wonder, then, that 

 the moon should raise a higher tidal wave than the 

 sun, and if this be the case with lunar attraction 

 there appears to be no reason why it may not be 

 assumed to be the case equally with lunar expansion. 

 The whole question, then, turns finally upon the 

 actual proportion which exists between the solar and 

 lunar powers of expansion; and it becomes necessary 

 to enquire what that proportion is. Is this propor- 

 tion so great that the 30th part of the lunar expan- 

 sion is greater than the 12000th part of the solar 

 expansion ? Now there is reason to believe that the 

 extreme range of solar heat may be 180 of Fah- 

 renheit (the range being from 60, which is the 

 lowest point to which the thermometer has fallen in 

 the polar regions, to + 130, which is the highest point 

 at which the mercury was noticed by MM. Lyon 

 and Ritchie, in the oasis of Mourzouk); and, there- 

 fore, if we assume that the lunar ray is as cold as 

 the coldest solar ray, we may suppose that the solar 



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