THE STORY OF NINETEENTH-CENTURY SCIENCE 



dency in Nature to the Dissipation of Mechanical En- 

 ergy." 



From the principle here expressed Professor Thomson 

 drew the startling conclusion that, " since any restora- 

 tion of this mechanical energy without more than an 

 equivalent dissipation is impossible," the universe, as 

 known to us, must be in the condition of a machine 

 gradually running down ; and in particular that the 

 world we live on has been within a finite time unfit for 

 human habitation, and must again become so within a 

 finite future. This thought seems such a commonplace 

 to-day that it is difficult to realize how startling it ap- 

 peared half a century ago. A generation trained, as 

 ours has been, in the doctrines of conservation and dis- 

 sipation of energy as the very alphabet of physical sci- 

 ence can but ill appreciate the mental attitude of a gen- 

 eration which for the most part had not even thought it 

 problematical whether the sun could continue to give 

 out heat and light- forever. But those advance thinkers 

 who had grasped the import of the doctrine of conser- 

 vation could at once appreciate the force of Thomson's 

 doctrine of dissipation, and realize the complementary 

 character of the two conceptions. 



Here and there a thinker like Rankine did, indeed, at- 

 tempt to fancy conditions under which the energy lost 

 through dissipation might be restored to availability, 

 but no such effort has met with success, and in time 

 Professor Thomson's generalization and his conclusions 

 as to the consequences of the law involved came to be 

 universally accepted. 



The introduction of the new views regarding the nat- 

 ure of energy followed, as I have said, the course of 

 every other growth of new ideas. Young and imagina- 



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