September 12, 1884.] 



SCIENCE, 



233 



link between the two. According to the other party, it 

 is to the difference of the chemical action of the metals 

 on the connecting liquid, that we must attribute the 

 rise and continuance of the electrical current. The 

 electromotive force of a voltaic cell is undoubtedly- 

 due to the intrinsic superficial manifestation of energy 

 when two dissimilar metals are placed in connection 

 with each other either directly or through the medium 

 of a conducting liquid. The chemical action of the 

 liquid brings new surfaces of the metals constantly 

 in contact; moreover, we have the difference of super- 

 ficial energy between the liquid and the metals, so 

 that our expression for electromotive force is far from 

 being a simple one: it contains the sum of several 

 modifications of superficial energy at the surfaces of 

 the two metals and at the two boundaries of the 

 liquid and the metals. 



We have again a development of electromotive 

 force by the mere contact of the metals at different 

 temperatures. The electrical current that arises is 

 due to the difference of superficial energy manifested 

 at the surface of the two junctions. We know that 

 the action is on the surface, for the size of the junc- 

 tions does not affect the electromotive force. Sup- 

 pose that we should make the metals so thin that 

 an ultimate molecule of iron should rest against an 

 ultimate molecule of copper, should we not arrive at 

 a limit, at a definite temperature of the conversion 

 of molecular vibration into electrical energy? And 

 also, when our theory is perfected of the number of 

 molecules along a linear line of copper against a 

 linear line of zinc which can produce a current of 

 electricity of a given strength, — the jostling, so to 

 speak, of these ultimate molecules of two metals at 

 different temperatures might form a scientific unit of 

 electromotive force in the future science of physical 

 chemistry. By means of an alloy we can apparently 

 modify the superficial energy at the surface of a solid. 

 Thus an alloy with a parent metal will give a varying 

 electromotive force. If we could be sure that an 

 alloy was always of a definite chemical composition, 

 and not a more or less mechanical admixture, it 

 seems as if we could get closer to the seat of elec- 

 tromotive force by a number of quantitative measure- 

 ments. Unfortunately, the physical nature of alloys 

 is not definitely known, and there is little coherence 

 or regularity in our measurements of their electro- 

 motive force. We can modify the superficial enenry 

 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. Professor Trowbridge is still engaged 

 upon researches of this nature; and, if the work is 

 not brilliant, he hopes that it will result in the ac- 

 cumulation of data for future generalization. 



The subject of thermo-electricity has been eclipsed 

 by the magnificent development of the dynamo-elec- 

 tric machines; but we may return to thermo-electri- 

 city as a practical source of electricity. Professor 

 Trowbridge has been lately occupied in endeavoring 

 to modify the difference of potential of thermo-electric 



junctions by raising one junction to a very high tem- 

 perature 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 electromotive force which re- 

 sults from the difference of superficial energy mani- 

 fested at the two junctions ? 



It is evident that our knowledge of electricity 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 regard to electricity, we 

 seldom reflect that gravitation is as great a mystery 

 as electrical attraction. What is the relation between 

 electricity and magnetism and gravitation and what 

 we call the chemical force of attraction ? 



The question of the connection between electricity 

 and gravitation dwelt much in Faraday's thoughts. 

 He failed, however, to find the slightest relation be- 

 tween gravitation and electricity; and he closes his 

 account of his experiments with these words: "Here 

 end my experiments on this subject for the present, 

 but I feel the conviction that there must be some 

 connection between electricity and gravitation." 

 Was the direction in which he experimented the true 

 direction to look for a possible relation? and cannot 

 the refined instruments and methods of the electrical 

 science of the present aid us in more promising lines 

 of research? If we could prove that whenever we 

 disturb the relative position of bodies, or break up 

 the state of aggregation of particles, we create differ- 

 ence of electrical potential ; and, moreover, if we could 

 discover that the work that this electrical potential 

 can perform, together with the heat that it developed 

 by the process, is the complete work that is done on 

 the system against attractive force, or as so-called 

 chemical attractive force, — we should greatly extend 

 our vision of the relation of natural phenomena. 

 And thus pursuing the line of argument of his address, 

 Professor Trowbridge ventured to state an hypothet- 

 ical law which it seemed to him is at least plausible: 

 That " whenever the force of attraction between 

 masses or molecules is modified in any way, a differ- 

 ence of electrical potential results." Is it not reason- 

 able to suppose that certain anomalies which we now 

 find in the determinations of specific heats of compli- 

 cated aggregation of molecules are due to our failure 

 to estimate the electrical equivalent of the movements 

 and interchanges of the molecules? Let us take the 

 case of friction between two pieces of wood : is it not 

 possible that the friction is the electrical attraction 

 which results from the endeavor to connect the phe- 

 nomenon of superficial energy with electrical mani- 

 festations, that the friction between two surfaces is 

 modified by keeping these surfaces at a difference 

 of electrical potential? In Edison's motophone, we 

 see this exemplified in a very striking manner. 



Professor Trowbridge's own studies have been 

 chiefly in the direction of thermo-electricity and in the 

 subject of the electrical aspect of what we call super- 

 ficial energy. These experiments so far deepen the 

 belief that any change in the state of aggregation of 



