116 HKLMHOLTZ OX THE CONSERVATION OF FORCE. 



must not ascribe qualitative differences, for when we speak of 

 different kinds of matter we refer to differences of action, that is, 

 to differences in the forces of matter. Matter in itself can there- 

 fore partake of one change only, — a change which has reference 

 to space, that is, motion. Natural objects are not, however, thus 

 passive ; in fact we come to a knowledge of their existence solely 

 from their actions upon our organs of sense, and infer from these 

 actions a something which acts. When, therefore, we wish to 

 make actual application of our idea of matter, we can only do it 

 by means of a second abstraction, and ascribe to it properties 

 which in the first case were excluded from our idea, namely the 

 capability of producing effects, or, in other words, of exerting 

 force. It is evident that in the application of the ideas of matter 

 and force to nature the two former should never be separated : 

 a mass of pure matter would, as far as we and nature are con- 

 cerned, be a nullity, inasmuch as no action could be wrought by 

 it either upon our organs of sense or upon the remaining portion 

 of nature. A pure force would be something which must have a 

 basis, and yet which has no basis, for the basis we name matter. 

 It would be just as erroneous to define matter as something which 

 has an actual existence, and force as an idea which has no corre- 

 sponding reality. Both, on the contrary, are abstractions from 

 the actual, formed in precisely similar ways. Matter is only 

 discernible by its forces, and not by itself. 



We have seen above that the problem before us is to refer 

 back the phaenomena of nature to unchangeable final causes. 

 This requirement may now be expressed by saying that for final 

 causes unchangeable forces must be found. Bodies with un- 

 changeable forces have been named in science (chemistry) ele- 

 ments. Let us suppose the universe decomposed into elements 

 possessing unchangeable qualities, the only alteration possible 

 to such a system is an alteration of position, that is, motion ; 

 hence, the forces can be only moving forces dependent in their 

 action upon conditions of space. 



To speak more particularly: the phaenomena of nature are 

 to be referred back to motions of material particles possessing 

 unchangeable moving forces, which are dependent upon con- 

 ditions of space alone. 



Motion is the alteration of the conditions of space. Motion, 



