30 DEVELOPMENT AND HEREDITY. 



then that way, by the resultant action of an almost 

 infinite number of forces, — forces of attraction, 

 repulsion, and gravitation, which extend toward us 

 from the extremest region of the stars and forever 

 change in form and in the endless complication of 

 their interaction. 



A mass of matter appears to be at rest, because 

 the forces which act upon its component particles are 

 in a state of equilibrium. As the forces emanating 

 from each particle act upon all the other particles, 

 no particle can be taken away or added without alter- 

 ing the statical condition of the whole mass and 

 changing the co-ordination of its form-conserving 

 forces, so that a new state of equilibrium must 

 result, in which each particle stands in a new rela- 

 tion to every other particle. Further, every change 

 in the external forces which act upon a mass of 

 matter must cause a change in the equilibrium of the 

 mass, necessitating either the movement of the mass 

 as a whole or some change in the internal relations 

 of its particles. This change in the relation of the 

 particles may be permanent or it may be temporary. 



These principles are fundamental, and they are so 

 important for our present inquiry that I quote here 

 a few illustrations of the subtle nature of the changes 

 produced upon inanimate matter by various forces, 

 and of the persistence of the effects. The first 



