Electromotive Force to Pressure Sfc, 109 



and an increase of electromotive force at that electrode ; the 

 three kinds of pressure — mechanical, chemical, and electrical — 

 varying directly together. The greater mechanical pressure 

 at the lower electrode enabled the liquid and metal to 

 chemically unite with greater energy, and thus permitted that 

 electrode to become electropositive to the other. The fact 

 that the strongest currents were usually obtained by the use 

 of the most energetic chemical substances further support the 

 view that the phenomenon is partly chemical, and it is well 

 known that certain substances will only chemically combine 

 whilst kept under pressure together. 



In all the cases in which the more positive metals, such as 

 zinc, were employed, both the electrodes were visibly corroded ; 

 as, however, the electric current was excessively minute, only 

 an extremely small proportion of this chemical action was 

 inseparably associated with it ; and as the currents were not 

 due to ordinary chemical heat, any examination of the com- 

 parative losses of weight of the two electrodes by corrosion 

 would probably have been of but little value. 



The phenomena suggest some abstruse questions, — What is 

 the most hidden cause of the current ? Only a very funda- 

 mental cause could have produced so large a proportion as 

 95 per cent, of currents in one uniform direction. The 

 original cause must lie in some change of the potential motion 

 of the molecules ; some kind of molecular energy must have 

 been lost in order to produce the currents. The immediate 

 cause was probably a small proportion of the potential energy 

 of the motion of the superficial molecules which must have 

 been transformed into current during chemical union of the 

 metal and liquid, the other and far greater portion being 

 directly changed into chemical heat. The questions why one 

 portion is directly converted into electric current and another 

 into heat, and why so largely into heat, I have not examined 

 (compare Proc. Roy. Soc. 1884, vol. xxxvi. p. 331 ; also 

 M. B. Raoult, Ann. de Chim. et de Phys. 1867, pp. 137-193). 



We know that work is done during the act of puttino- on 

 the pressure, and that this work may increase the energy of 

 molecular motion; in addition to the energy communicated 

 to the arrangement in this way, constant pressure may pro- 

 duce constant current if there is a continual yielding of the 

 molecules to it ; but as only motion can produce motion, and 

 as unchanging pressure is a purely statical phenomenon, if 

 there is no such yielding unvarying pressure cannot be a real 

 cause of continuous current. We know also that the properties 

 of substances and the molecular motions to which those 



