554 THE POPULAR SCIENCE MONTHLY. 



tension, which determines 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 stop- 

 page of motion, into a certain quantity of heat, this something is a 

 reality, distinct 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 independence 

 and preeminence of force, nor so completely includes the assertion of 

 the essential reality of a cause preexisting motion. The idea of force 

 is one of those elementary forms of thought from which we cannot 

 escape, because it is the necessary conclusion, the fixed and undestroy- 

 able 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 theorem or experiment ; it knows it, it 

 clings to it by natural and unconquerable affinity. We must say of 

 force what Pascal said of certain fundamental notions of the same 

 order: "Urging investigation further and further, we necessarily 

 arrive at primitive words which cannot be defined, or at principles so 

 clear that we can find no others which are clearer." When we have 

 reached these principles, nothing remains but to study one's self with 

 profoundest meditation, not striving to give an image to those things 

 whose essence is that they cannot be imagined. From the most gen- 

 eral and abstract point of view, then, matter is at once form and force, 

 that is, there is no essential difference between these two modes of 

 substance. Form is simply force circumscribed, condensed. Force is 

 simply form indefinite, diffused. Such is the net result of the method- 

 ical inquiries of modern science, and one which forces itself on our 

 minds, apart from any systematic premeditation. It is of consequence 

 to add that the merit of having formulated it very clearly and noted 

 its importance belongs to French contemporary philosophers, particu- 

 larly to Charles Leveque and Paul Janet. 



II. 



If the web of things, the essence of matter, is one single substance, 

 who was the Orpheus under whose spell these materials gathered, 

 ranged, and diversified themselves into natures of so many kinds ? 

 And, first of all, how can the extension of bodies proceed from an 

 assembling of unextended principles ? The answer to this first ques- 

 tion docs not seem difficult to us. Extension exists prior to matter. 

 They are two distinct things, without any relation of causality or 



