ARMY SURGEON AT POTSDAM 41 



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 not to 

 refer back the phenomena 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 unchangeable forces have been named in science 

 (chemistry) elements. Let us suppose the universe decom- 

 posed 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 only be moving 

 forces dependent in their action upon conditions of space. 



' To speak more particularly : the phenomena of nature are 

 to be referred back to motions of material particles possessing 

 unchangeable moving forces, which are dependent upon condi- 

 tions of space alone. Motion is the alteration of the conditions 

 of space. Motion, as a matter of experience, can only appear 

 as a change in the relative position of at least two material 

 bodies. Force, which originates motion, can only be conceived 

 of as referring to the relation of at least two material bodies 

 towards each other; it is therefore to be defined as the 

 endeavour of two masses to alter their relative position. But the 

 force which two masses exert upon each other must be resolved 

 into those exerted by all their particles upon each other ; hence 

 in mechanics we go back to forces exerted by material points. 

 The relation of one point to another, as regards space, has 

 reference solely to their distance apart : a moving force, there- 

 fore, exerted by each upon the other, can only act so as to 

 cause an alteration of their distance, that is, it must be either 

 attractive or repulsive. 



' Finally, therefore, we discover the problem of physical 

 natural science to be, to refer natural phenomena back to 

 unchangeable attractive and repulsive forces, whose intensity 



