THE EARTH'S INTERIOR HEAT. 301 



passed through a great space in a straight line, or after pre- 

 vious central motion round it, is, according to the laws devel- 

 oped in relation to the sun in Chapter III., confined within 

 the limits of 7908 and 11,183 metres. The heat generated 

 by this process may amount to from 8685 Xx to 1 7,370 Xa 

 units, according to the value of the major axis of the orbit 

 of x. This heat, however, vanishes by its distribution through 

 the greater mass, because x is, according to supposition, infi- 

 nitely small in comparison with T. 



The quantity of heat generated increases with #, and 

 amounts in the second case, when x = % T, to from 6000 X T 

 to 8685XT units. 



If we assume the earth to possess a very great capacity 

 for heat, equal in fact to that of its volume of water, which 

 when calculated for equal weights = 0*184, the above discus- 

 sion leads to the conclusion that the difference of temperature 

 of the constituent parts, and of the earth after their union, or, 

 in other words, the heat generated by the collision of these 

 parts, may range, according to their relative magnitude, from 

 to 32,000, or even to 47,000 ! 



With the number of parts which thus mechanically com- 

 bine, the quantity of heat developed increases. Far greater 

 still would have been the generation of heat if the constituent 

 parts had moved in separate orbits round the sun before their 

 union, and had accidentally approached and met each other. 

 For various reasons, however, this latter supposition is not 

 very probable. 



Several facts indicate that our earth was once a fiery 

 liquid mass, which has since cooled gradually, down to a com- 

 paratively inconsiderable depth from the surface, to its pres- 

 ent temperature. The first proof of this is the form of the 

 earth. " The form of the earth is its history." According 

 to the most careful measurements, the flattening at the poles 

 is exactly such as a liquid mass rotating on its axis with the 

 velocity of the earth would possess ; from this we may con- 



