110 Dr. G. Gore on the Relation of Volta 



properties are due vary with every change of mechanical 

 pressure. If, therefore, pressure alters the direction or the 

 velocity of molecular motion, it may act as a permitting con- 

 dition so as to enable some of the unceasing motion of the 

 molecules to expend itself in producing a permanent current, 

 like such motion does in a voltaic cell ; and this appears to 

 be a reasonable explanation. Contraction of total volume by 

 chemical union, being a yielding to pressure, may contribute 

 to the result in the present case. 



As the production of current was conditional upon difference 

 of pressure at the two electrodes, it must have been as much 

 dependent upon the pressure and the state of molecular motion 

 at one electrode as upon that at the other. And as we know 

 that volta electromotive force is very intimately connected 

 with velocity of the molecules, and that the two appear to 

 vary directly together (see " A General Relation of Electro- 

 motive Force to Equivalent Volume and Molecular Velocity," 

 Proc. Birm. Phil. Soc. 1892, vol. viii. pp. 63-138 ; The 

 Electrical "Review, vol. xxx. pp. 693, 722, 755, 786 ; and 

 Phil. Mag. Sept. 1892, p. 307), it is probable that the greater 

 degree of pressure at the lower electrode permits some of the 

 molecules of liquid and metal to strike each other with greater 

 velocity than at the upper one. It is worthy of notice that pres- 

 sure has the same effect as dilution of the electrolyte, &c. upon 

 volta electromotive force (ibid.) ; as dilution and pressure each 

 separately increases volta electromotive force, and as dilution 

 is apparently attended by an increase of velocity of the mole- 

 cules, it is reasonable to conclude that pressure is probably 

 attended by a similar effect. It would be interesting to in- 

 vestigate the relations of the current to the compressibility and 

 elasticity of metals and electrolytes. The present results 

 indicate that electromotive force may be due to unequal mole- 

 cular pressure. 



Whatever may be the manner in which the molecular 

 motions are affected by pressure, whether by altering their 

 direction or their velocity, the experiments of this research 

 show that they are influenced in essentially the same way in 

 39 out of 41 instances, and it is evident that only some very 

 fundamental cause could produce such a uniform effect. The 

 fact that nearly all the currents are in one direction suggests 

 that the real cause of electromotive force itself can only be 

 about one stage more fundamental than the cause of the 

 currents. In all cases the currents obtained were results, not 

 only of a difference of electromotive force between the lower 

 metal and liquid and the upper ones, but primarily of the 



