16 THE STORY OF LIFE'S MECHANISM. 



rather than a statical, should ensue. Modern 

 biology was the child of historical geology. 



But historical geology alone could never have 

 led to the dynamical phase of modern biology. 

 Three other conceptions have contributed in an 

 even greater degree to the development of this 

 science. 



CONSERVATION OF ENERGY. 



The first of these was the doctrine of conserva- 

 tion of energy and the correlation of forces. This 

 doctrine is really quite simple, and may be out- 

 lined as follows : In the universe, as we know it, 

 there exists a certain amount of energy or power 

 of doing work. This amount of energy can 

 neither be increased nor decreased ; energy can 

 no more be created or destroyed than matter. It 

 exists, however, in a variety of forms, which may 

 be either active or. passive. In the active state it 

 takes some form of motion. The various forces 

 which we recognize in nature heat, light, elec- 

 tricity, chemism, etc. are simply forms of 

 motion, and thus forms of this energy. These 

 various types of energy, being only expressions 

 of the universal energy, are convertible into each 

 other in such a way that when one disappears 

 another appears. A cannon ball flying through 

 the air exhibits energy of motion ; but it strikes 

 an obstacle and stops. The motion has appar- 

 ently stopped, but an examination shows that 

 this is not the case. The cannon ball and the 

 object it strikes have been heated, and thus the 

 motion of the ball has simply been transformed 

 into a different form of motion, which we call 



