HELMHOLTZ ON THE CONSERVATION OF FORCE. 115 



nature may be referred to, and deduced from, general rules. These 

 rules, — for example, the law of the reflexion and refraction of 

 light, the law of Mariotte and Gay-Lussac regarding the volumes 

 of gases, — are evidently nothing more than general ideas by 

 which the various phaenomena which belong to them are con- 

 nected together. The finding out of these is the office of the 

 experimental portion of our science. The theoretic portion seeks, 

 on the contrary, to evolve the unknown causes of the processes 

 from the visible actions which they present ; it seeks to compre- 

 hend these processes according to the laws of causality. We 

 are justified, and indeed impelled in this proceeding, by the con- 

 viction that every change in nature must have a sufficient cause. 

 The proximate causes to which we refer phaenomena may, in 

 themselves, be either variable or invariable ; in the former case 

 the above conviction impels us to seek for causes to account for 

 the change, and thus we proceed until we at length arrive at 

 final causes which are unchangeable, and which therefore must, 

 in all cases where the exterior conditions are the same, produce 

 the same invariable effects. The final aim of the theoretic 

 natural sciences is therefore to discover the ultimate and un- 

 changeable causes of natural phaenomena. Whether all the pro- 

 cesses of nature be actually referrible to such, — whether nature 

 is capable of being completely comprehended, or whether changes 

 occur which are not subject to the laws of necessary causation, 

 but spring from spontaneity or freedom, this is not the place to 

 decide ; it is at all events clear that the science whose object it 

 is to comprehend nature must proceed from the assumption that 

 it is comprehensible, and in accordance with this assumption 

 investigate and conclude until, perhaps, she is at length admo- 

 nished by irrefragable facts that there are limits beyond which 

 she cannot proceed. 



Science regards the phaenomena of the exterior world according 

 to two processes of abstraction : in the first place it looks upon 

 them as simple existences, without regard to their action upon 

 our organs of sense or upon each other; in this aspect they are 

 named matter. The existence of matter in itself is to us some- 

 thing tranquil and devoid of action : in it we distinguish merely 

 the relations of space and of quantity (mass), which is assumed 

 to be eternally unchangeable. To matter, thus regarded, we 



