358 COSMIC rillLOSOrilY. [pt. il 



Btars. Similar conclusions are indicated by the observed 

 geologic features of Mars and Venus ; and in the case of the 

 moon we shall presently see what a prodigious loss of heat 

 is implied by the fact that the forces which once upheaved 

 its great volcanoes are now quiescent. The sun, too, is 

 pouring away heat at such a rate that, according to Sir John 

 Herschel, if a cylinder of ice 184,000 miles in length and 

 45 miles in diameter were darted into the sun every second, 

 it would be melted as fast as it came. Or, as Mayer has 

 calculated, the amount of heat lost every minute by the sun 

 would suffice to raise the temperature of thirteen billion 

 cubic miles of water one degree Centigrade. Although this 

 prodigious loss is perhaps partly compensated by heat due 

 to the arrested motion of meteors falling upon the sun's 

 surface, yet it is by no means probable that it is in this way 

 compensated to any noteworthy extent. It is in every way 

 indisputable that from time immemorial sun, moon, and 

 earth, as well as the other members of our system, have 

 been parting with their internal motion, in the shape of heat 

 radiated into surrounding space. 



Thus in the history of our planetary system we may 

 already begin to witness that dissipation of motion which 

 has been shown to be one of the prime features of the process 

 of Evolution, wherever exemplified. But, as we have also 

 seen, the dissipation of motion is always and necessarily 

 accompanied by the concentration of matter. It is not 

 simply that, with two or three apparent exceptions, which 

 have no bearing upon the present argument, all cooling 

 bodies diminish in size and increase in density ; but it is 

 also that all contracting bodies generate heat, the loss of 

 which, by radiation, allows the process of contraction to 

 continue. In any contracting mass the particles which tend 

 toward the common centre have their molar motions con- 

 stantly opposed by friction upon each other, and most of the 

 motion thus arrested is converted into heat. If this heat ia 



