Hypothesis of the Internal Fluidity of the Earth. 133 



more intense. The cubic contents of the earth amount to 



about 259,431,755,889 



miles, from which deducting that part of 



which the temperature is under 212°, 295,219,500 



miles, we have 259,136,536,389 



cubic miles of a temperature exceeding that of boiling water. 

 From this it appears that the proportion which that part of 

 the globe of which the temperature is below 212° bears to 

 that possessed of higher degrees of heat, is as one to 878 

 nearly. In like manner, the proportion which that part of 

 the earth's mass possessed of a temperature of 752° or under 

 bears to that of a higher temperature, is as one to 218. 



2. Cast iron fuses at about 2786° Fahr. Taking the pre- 

 sent mean temperature of the whole surface of the earth at 

 67°, the temperature of molten cast iron will, according to the 

 foregoing assumptions, be reached at a depth of 40,785 yards, 

 or 23*173 miles. This, then, would be the average thickness 

 of the solid crust of the earth at present, supposing the 

 materials of which it consists to possess about the same 

 degree of fusibility as cast iron- By descending 45,000 

 yards, or 25-56 miles, we should experience an increase of 

 heat amounting to 3000° Fahr. At such a depth the tem- 

 perature (3067°) wo aid probably be sufficient to hold in a 

 state of fusion by far the greater part of such substances as 

 there exist, unless, which is by no means probable, they are 

 much more infusible than the great bulk of the substances 

 composing that part of the crust with which we are more 

 intimately acquainted. 



3. Since (by hypothesis) the whole earth was at one time 

 in a molten state, let us assume that the surface temperature 

 was then 3067° or 3000° more than the mean surface tem- 

 perature at present. In order, then, that the crust should be 

 cooled down to its present state, it would require to part 

 with an amount of heat equal to 3^o° or 1500° upon the 

 whole, the upper surface losing 3000° of heat, and the lower 

 or interior surface nil. 



4. The contraction resulting from refrigeration would 

 necessarily shorten the earth's radius. To ascertain the 

 amount of such shortening, let it be granted that the materials 



