AND ITS SELF-CONSERVATION. 133 



a careful consideration of the accepted "laws of motion" 

 will lead us toward the full development of that condition 

 and of its central significance. 



FIRST LAW OF MOTION. 



This law was formulated by Newton as follows: 

 " Every body continues in its state of rest or of uniform 

 motion in a straight line, except in so far as it may be 

 compelled by impressed forces to change that state." * 



We have, indeed, already developed the complete jus- 

 tification of this law which is absolutely universal since 

 it is implied in the very nature of the extended world. It 

 cannot, therefore, be classed under the category of * ' rela- 

 tive knowledge," though it affirms that without external 

 relations any and every single body is absolutely helpless 

 and inane. 



But the law, in affirming the absolute incapacity of an 

 isolated body either to move itself, or in any way to 

 change the direction or quantity of motion which may 

 have been imparted to it, expresses a most significant 

 limitation of extended objects. The law does not affirm 

 a positive characteristic of the external world, but a 

 wholly negative one. It does not declare what material 

 objects possess. On the contrary it declares unquestion- 

 ably what they do not possess, and that is the power of 

 self-movement. Every body, every object in the material 

 universe, moves, or changes the direction or velocity of 

 its motion only from external causes. Such body can act 

 only in so far as it is acted upon. 



This law is then very appropriately styled the law of 

 Inertia, which is in truth nothing else than the law of 



* This, with the statement of the second and third laws, given below, is 

 the rendering of Newton's Latin given by Thompson and Tait. 



