20 Results of the Contraction of a Solid Globe. 



the surface-temperature aV 2 ; so that, if we put the surface- 

 temperature at 50°, it is at present 124° F., and, since it varies 

 as \/t, low as this value may seem, it is higher now than it 

 has ever been. 



The depth of the level of no strain is j into the excess of 



temperature, or 51 x 74*56 feet. 



Hence the depth of the level of no strain is now 3802 feet, 

 or about 0*7 of a mile. 



The radial contraction ccV 2 , and will therefore be 2 miles. 



Lastly, 



9 a 3 



since h = e -r-3, 



4 r 



h oc $ and -j- oc sjt. 

 at 



This shows that the rate at which mountains would be 

 formed is proportional to the square root of the time, and 

 ought therefore to be greater at present than at any previous 

 period. 



Collecting our results, we may say that, on ihe two suppo- 

 sitions made respecting the temperature of solidification, we 

 should have, at the present time : — 



Temperature of Solidification... 



7000° F. 



4000° F. 



Depth of level of greatest cooling*... 



54 miles. 

 2 miles. 

 258° F. 

 19 feet. 

 6 miles. 



31 miles. 

 07 mile. 



124° F. 



2 feet. 

 2 miles. 



Temperature of level of no strain . . . 

 Mean height of elevations 





It must be admitted, from the general bearing of the fore- 

 going results, that the important discovery of the existence 

 of a level of no strain in a solid globe, cooling by conduc- 

 tion, renders more than ever untenable the theory that the 

 surface-elevations can have been formed b} r the compression 

 of the crust of a solid globe caused in that manner. An 

 inversion of the Horatian line would seem fairly to describe 

 that theory — 



Nascuntur monies, genuit qnos ridiculus mus. 



* See Prof. Darwin's letter, 'Nature,' Feb. 6, 1879. 



