WHAT IS ELECTRICITY ? 85 



heats it with its contained water, we have not only the heated water 

 but also an electrical current ; it is evident, therefore, that we should 

 be able to heat the water more when the wire between the two vessels 

 is cut, than when there is a metallic circuit between them, for a part 

 of the energy of the falling weight has become converted into an elec- 

 trical current. At the terminals of the cut wires there is a difference 

 of electrical potential created for an instant, which, however, instantly 

 disappears. What is the equivalent of the disappearance of this dif- 

 ference of potential ? Is it not in the closed circuits through the 

 masses of the metals, a part of which, it is true, becomes sensible heat, 

 but another portion may become latent heat or do internal work 

 among the molecules ? 



Moreover, is it not reasonable 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 mole- 

 cules ? Let us take, again, 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 move the adjoining particles of 

 wood in the two pieces asunder ? Let us remember, in our endeavor 

 to connect the phenomenon of superficial energy with electrical mani- 

 festations, that the friction between two surfaces is modified by keej)- 

 ing these surfaces at a difference of electrical potential. In Edison's 

 motophone, by means of which the voice of one speaking in New York 

 could be made audible to this audience, we see this exemplified in a 

 very striking manner. A platinum point connected with one pole of 

 a battery rubs upon a revolving cylinder of chalk, which is simply 

 moistened with water and is connected with the opposite pole of the 

 battery. The friction between the two is modified in unison with the 

 changes in electrical potential of the battery ; and a diaphragm in con- 

 nection with the platinum point responds to these changes in the fric- 

 tion, and therefore to a transmitter placed anywhere in the electrical 

 circuit. 



My own studies have been chiefly in the direction of thermo-elec- 

 tricity, and in the subject of the electrical aspect of what we call super- 

 ficial energy. I think there is a great field here — in which a large crop 

 of negative results can be reaped — but these negative results I can not 

 regard entirely as thistles. I have tried the following experiment, on 

 the hypothesis that an electrical difference of potential in changing the 

 relations of molecules might modify the heat that is radiated from a 

 surface. I have endeavored to discover whether an electrical current 

 first cools a conductor before it heats it, as we might expect if the 

 molecules being restrained in any way could not radiate as much en- 

 ergy into space as they could under the same difference of temperature, 

 when not submitted to the action of an electrical difference of potential. 

 I have reaped only a thistle so far from this investigation, but I shall 



