278 THE POPULAR SCIENCE MONTHLY. 



knowledge so modified the notation of chemistry that the new formu- 

 las, though differing but slightly from the old, represented more than 

 composition by weight, namely, composition by volume also. Still 

 later came the attempt, now being vigorously continued, to make 

 every formula represent not only ultimate composition by weight and 

 by volume, but also the probable arrangement of the atoms within 

 the molecule. In other words, if we ignore the atomic hypothesis, a 

 modern chemical formula aims to express some of the more important 

 chemical relations and reactions of the body represented. In close 

 connection with these purely chemical discoveries, we find a little 

 physical work. Thanks to Kopp, we are able to calculate from the 

 formula of almost any liquid its atomic volume, and thence its specific 

 gravity at the boiling-point. Other investigators enable us to cal- 

 culate the indices of refraction for different liquids, and, to a more 

 limited extent, some other physical properties also. In short, a system 

 of notation, originally based upon the properties of the atoms as regards 

 weight, has been found to express also many of their other physical 

 relations ; and the list of facts thus expressed is continually lengthen- 

 ing. Evidently, then, the tendency of chemical investigation is to 

 connect the physical properties of every substance directly with its 

 composition. 



Here we step over the border into physics. Plainly, if we have to 

 deal with physical properties, we must study the forces represented by 

 them. And, fortunately for the chemist, the tendency among physi- 

 cists is entirely in his favor. Growing up contemporaneously with 

 the development of chemical notation, we have had the grand ideas 

 of the conservation of energy and the correlation of forces. We have 

 learned that force is one, indestructible and uncreatable, and that all 

 its manifestations are mutually convertible one into another. Either 

 of the great modes of force may be active in affecting chemical com- 

 position ; may cause chemical union or chemical separation ; may be 

 the motive of either analysis or synthesis. Now, in the direction here 

 suggested, the main work of physics is being done. The chief object 

 of the physicist to-day is to determine quantitatively the relations 

 connecting all the different varieties of energy. Under what circum- 

 stances, and how, are forces transformed ? Since these transformations 

 are differently effected through the intervention of different forms of 

 matter, it is clear that the physicist must take into account the chemi- 

 cal composition of the materials with which he deals. In short, then, 

 the chemist must look to physics for a knowledge of the forces in- 

 volved in chemical changes ; while, on the other hand, the science of 

 physics must needs throw from chemistry its information upon the 

 nature of all the material agencies through which the transformations 

 of force become apparent. Neither physics nor chemistry can work 

 independently of the other; the more closely they become allied in 

 the labor of investigation, the more rapidly will both progress. The 



