ii4 POPULAR LECTURES AND ADDRESSES. 



PART II. ON THE ORIGIN AND TOTAL AMOUNT 

 OF PLUTONIC ENERGY. 



30. By Plutonic action, I mean any disturbance 

 of underground equilibrium. Volcanoes, earth- 

 quakes, and subsidences are the phenomena most 

 commonly understood when plutonic activity is 

 spoken of. The store of energy to which these 

 phenomena arc clue is properly called plutonic 

 energy, and according to the clear and simple, but 

 thoroughly rigorous, language of modern dy- 

 namics, plutonic energy is to be distinguished 

 from plutonic activity. 



31. The action of a dynamical agent was defined 

 by Newton, as something to be measured numeri- 

 cally, by the number measuring simple force or 

 pressure, multiplied into the number measuring 

 the velocity with which the matter experiencing 

 it yields in the direction of the force. In the 

 nineteenth century dynamical vocabulary, Newton's 

 " action of an agent " is simply a performing of 



