6oo POPULAR SCIENCE MONTHLY. 



gation then we should have the material for illustrating at least 

 one side of electricity mechanically. It may, indeed, be said 

 here with certainty that only one side is considered, and that 

 here also the defectiveness, without exception, of all mechanical 

 hypotheses is demonstrated, and the full completion of the figure 

 prevented. 



When we have really traced the laws of natural phenomena 

 back to the laws of corresponding kinds of energy, what advan- 

 tage have we gained ? First, the very important point that a sci- 

 ence free from hypothesis is possible. We inquire no longer for 

 forces which we can not exhibit, acting between atoms which we 

 can not observe, but we ask, when we would judge respecting a 

 process, concerning the kind and number of the energies going 

 into it and issuing from it. We can measure them, and all that it 

 is necessary to know can be expressed in that form. How enor- 

 mous a methodical advantage that is will be clear to everybody 

 whose scientific conscience has suffered from the unceasing amal- 

 gamation of fact and hypothesis which the physics and chemistry 

 of the present offer as rational science. The energistic is the way 

 in which Kirchhoff's variously misunderstood demand for replac- 

 ing what is called the theory of Nature by the description of phe- 

 nomena can be fulfilled in its right sense. With this freedom from 

 hypothesis of energistic science is at the same time associated a 

 simplicity which, it can be said without hesitation, has not been 

 reached before. I have already pointed to the philosophical sig- 

 nificance of this simple principle in the comprehension of natural 

 phenomena. It lies in the nature of the matter, but might also 

 well be declared on other considerations, that an immense advan- 

 tage will result to the teaching and comprehension of science by 

 means of this philosophical simplification. To cite only one ex- 

 ample, we might assert that all equations, without exception, 

 which relate two or more different kinds of phenomena to one 

 another, must be equations between magnitudes of energy, else 

 they are not possible. This is a consequence of the fact that 

 besides the conceptions space and time, energy is the only entity 

 that is common to the different fields, and in fact to all, with- 

 out exception ; comparisons can not be made between different 

 fields otherwise than by the portions of energy that come into 

 question. 



I shall have to refrain from showing here how an immense 

 number of relations, a part of which were already known and a 

 part are new, can be immediately written down by means of this 

 view, while formerly they had to be deduced by more or less de- 

 tailed calculations. I can not either set before you in comparison 

 the new sides which other already, if not so perfectly known 

 propositions of thermodynamics, the most extended part of ener- 



