82 THE POPULAR SCIENCE MONTHLY. 



to the seat of electro-motive force by a number of quantitative meas- 

 urements. Unfortunately, the physical nature of alloys is not defi- 

 nitely known, and there is little coherence or regularity in our measure- 

 ments of their electro-motive force. Still, there is a great field in the 

 study of the electro-motive force of alloys. We can modify the super- 

 ficial energy of metals, not only by melting metals together, but also by 

 grinding them to a very fine powder, and compressing them again by 

 powerful means into solids more or less elastic, and then examining 

 their superficial energy, which is manifested as electro-motive force. 

 I am still engaged upon researches of this nature, and, if the work 

 is not brilliant, I hope that it will result in the accumulation of data 

 for future generalization. 



We can not treat the manifestation of electro-motive force in the 

 voltaic cell apart from the manifestation of electro-motive force in the 

 differently heated junctions of a thermo-electric junction. In both 

 cases there is a difference of manifestation of superficial energy ; and 

 in thermo-electricity we can also modify this energy by making alloys. 

 The subject of thermo-electricity has been eclipsed by the magnificent 

 development of the dynamo-electric machine, but we may return to 

 thermo-electricity as a practical source of electricity. I have been 

 lately occupied in endeavoring to modify the difference of potential 

 of two thermo-electric junctions, by raising one junction to a very 

 high temperature under great pressure ; for it is well known that the 

 melting-point of metals is raised by great pressure. If the metal still 

 remains in the solid state under great temperature and great pressure, 

 can we not greatly increase the electro-motive force which results 

 from the difference of superficial energy manifested at the two junc- 

 tions ? 



When an electrical current is passed through two thermo-electric 

 junctions, it cools the hot one and heats the cool one. Moreover, you 

 are well acquainted with Thomson's discovery that a current of elec- 

 tricity, in passing through a metal, carries heat, so to speak, with it — 

 in one direction in iron and in another in copper. Do we not see here 

 a connection between the manifestation of superficial energy in liquids 

 and the effect of a difference of potential upon it, and the manifes- 

 tations of thermo-electro-motive force and the effect of differences 

 of electrical potential? It is curious and suggestive that, in applying 

 the reasoning of Carnot's cycle to the effect of a difference of electri- 

 cal potential on the superficial energy at the surface of separation 

 of two liquids, one is led to the equations which express in thermo- 

 dynamics the Peltier and Thomson effects. 



In thus looking for the seat and origin of electrical action, how 

 much have we discovered ? It is evident that our knowledge of elec- 

 tricity will increase with our knowledge of molecular action, and our 

 knowledge of molecular action with that which we call attractive 

 force. It is somewhat strange that, although we are so curious in 



