NOMOS. 129 



after the rate which has been ^specified. If we ask 

 this question, the answer is that the radius must 

 expand 1209 feet for every degree of 

 Fahrenheit, an amount which is equal ^twm" 

 to no less than 2 '2 9 miles for ten degrees cause the 



~ , i earth to ex- 



of the same scale. Such must be the 



rate of expansion in such an earth under 



this trifling elevation of temperature ; 



and, great though it be, it is not half so great as it 



would be if the imaginary earth were formed of 



sandstone instead of granite. 



It does not follow, however, that the actual earth 

 ought to expand at this rate, or in any degree ap- 

 proximating to this rate. In the ideal case, the earth 

 is one unbroken mass of granite ; in the actual case, 

 there is much water, and the land is made up of 

 fragments and particles with innumerable interstices. 

 In the ideal case, that is to say, there is nothing to 

 mask the law of expansion, for it is not easy to sup- 

 pose that this law should be modified by the mere 

 size of the body expanding ; but in the actual case 

 there is much to mask the law of expansion. There 

 is much to mask this law, partly because the water 

 which covers so large a portion of the surface will 

 expand into a volatile vapour, and partly because a 

 great part of the expansion of the land must be 

 expended in the filling up of the interstices which 

 separate the fragments and particles of which the 

 land is composed. And thus it is possible to see in 

 these interstices, not so much waste space, but a 

 provision for balancing the expansibility of the 

 earth, a provision which is precisely similar to that 



K 



