12 NATURE AND LIFE. 



compare its primal activities with the only activity of 

 which we have direct knowledge and intuition, that is to 

 say, with that admirable spring of will, so prompt and sure, 

 which permits us every moment to create and also to guide 

 motion. 



Motion may serve to measure force, but not to explain 

 it. It is as subordinate to the latter as speech is to thought. 

 In truth, motion is nothing else than the series of successive 

 positions of a body in different points of space. Force, on 

 the other hand, is the tendency, the tension, which deter- 

 mines the body to pass continually from one to the other 

 of these points ; that is to say, the power by which this 

 body, considered at any instant in its course, differs from 

 the identical body at rest. Evidently this something which 

 is in one of these two bodies and is not in the other, this 

 something that mathematicians call the quantity of motion, 

 which is transformed, on a sudden stoppage of motion, into 

 a certain quantity of heat, this something is a reality, dis- 

 tinct from the trajectory itself ; and yet nothing, absolutely 

 nothing, outside of the inner revelation of our soul, gives 

 us the means of understanding what this initial cause of 

 the motive forces may be. The distinguished founder of 

 the mechanical theory of heat, Robert Mayer, defines force 

 to be " whatever may be converted into motion." There 

 is no formula that so well expresses the fact of the inde- 

 pendence and preeminence of force, or so completely in- 

 cludes the assertion of the essential reality of a cause pre- 

 existing motion. The idea of force is one of those ele- 

 mentary forms of thought from which we cannot escape, 

 because it is the necessary conclusion, the fixed and unde- 

 stroyable residue from the analysis of the world in the 

 alembic of our minds. The soul does not find it out by 

 discursive reasoning, nor prove it to itself by way of theo- 

 rem or experiment ; it knows it, it clings to it by natural 

 and unconquerable affinity. We must say of force what 



