ON THE SUN'S HEAT. 415 



converted by thermodynamics into a necessary 

 truth, if we make no other uncertain assumption 

 than that the materials at present constituting the 

 dead matter of the solar system have existed under 

 the laws of dead matter for a hundred million 

 years. Thus there may in reality be nothing more 

 of mystery or of difficulty in the automatic pro- 

 gress 'of the solar system from cold matter diffused 

 through space, to its present manifest order and 

 beauty, lighted and warmed by its brilliant sun, 

 than there is in the winding up of a clock x and 

 letting it go till it stops. I need scarcely say that 

 the beginning and the maintenance of life on the 

 earth is absolutely and infinitely beyond the range 

 of all sound speculation in dynamical science. 

 The only contribution of dynamics to theoretical 

 biology is absolute negation of automatic com- 

 mencement or automatic maintenance of life. 



I shall only say in conclusion : Assuming the 

 sun's mass to be composed of materials which 



1 Even in this, and all the properties of matter which it involves, 

 there is enough, and more than enough, of mystery to our limited 

 understanding. A watch-spring is much farther beyond our 

 understanding than is a gaseous nebula. 



