NATURE 713 



the higher order, and that the mutual destruction of these terms will 

 be rigorous and absolute. 



The Present State of Physics. Two opposite tendencies may be 

 distinguished in the history of the development of physics. On the 

 one hand, new relations are continually being discovered between 

 objects which seemed destined to remain forever unconnected ; scattered 

 facts cease to be strangers to each other and tend to be marshalled 

 into an imposing synthesis. The march of science is towards unity 

 and simplicity. 



On the other hand, new phenomena are continually being revealed; 

 it will be long before they can be assigned their place sometimes it 

 may happen that to find them a place a corner of the edifice must be 

 demolished. In the same way, we are continually perceiving details 

 ever more varied in the phenomena we know, where our crude senses 

 used to be unable to detect any lack of unity. What we thought to 

 be simple becomes complex, and the march of science seems to be 

 towards diversity and complication. 



Here, then, are two opposing tendencies, each of which seems to 

 triumph in turn. Which will win? If the first wins, science is pos- 

 sible; but nothing proves this a priori, and it may be that after un- 

 successful efforts to bend Nature to our ideal of unity in spite of her- 

 self, we shall be submerged by the ever- rising flood of our new riches 

 and compelled to renounce all idea of classification to abandon our 

 ideal, and to reduce science to the mere recording of innumerable 

 recipes. 



In fact, we can give this question no answer. All that we can do 

 is to observe the science of to-day, and compare it with that of yes- 

 terday. Xo doubt after this examination we shall be in a position to 

 offer a few conjectures. 



Half-a-century ago hopes ran high indeed. The unity of force had 

 just been revealed to us by the discovery of the conservation of energy 

 and of its transformation. This discovery also showed that the phe- 

 nomena of heat could be explained by molecular movements. Although 

 the nature of these movements was not exactly known, no one 

 doubted but that they would be ascertained before long. As for light, 

 the work seemed entirely completed. So far as electricity was con- 

 cerned, there was not so great an advance. Electricity had just an- 

 nexed magnetism. This was a considerable and a definitive step 

 towards unity. But how was electricity in its turn to be brought into 

 the general unity, and how was it to be included in the general uni- 

 versal mechanism? No one had the slightest idea. As to the possi- 

 bility of the inclusion, all were agreed ; they had faith. Finally, as 

 far as the molecular properties of material bodies are concerned, the 

 inclusion seemed easier, but the details were very hazy. In a word, 

 hopes were vast and strong, but vague. 



