METHODS OF ELECTRICAL STIMULATION 37 



with the electrolyte, an immeasurably thin layer 

 of positively electrified molecules may be said to 

 coat its surface, and in the electrolyte a parallel 

 layer of negatively electrified molecules will 

 collect. On every side of the parallel layer 

 electricity of the same sign will be repelled. In 

 the case of a liquid metal, for example mercury, 

 the form of the surface will be altered, for the 

 repulsion of like electricities will tend to stretch 

 the surface layer, and will thus oppose the sur- 

 face tension. The new form which the surface 

 will take is the equilibrium between the electri- 

 cal energy and the surface tension (Helmholtz). 

 If this equilibrium is changed by the introduc- 

 tion of new electrical energy, the curvature of 

 the surface will change (Henry). 



Fasten an iron wire in the muscle clamp and 

 clamp the latter to the stand. Bring the wire 

 over the mercury and lower the muscle clamp 

 until the wire just touches the edge of the 

 mercury. Fix the clamp in this position. 



The instant the two metals touch (iron and 

 mercury in chromic acid solution) the existing 

 difference of potential will be altered. The sur- 

 face tension will thereby be increased and the 

 globule will become more convex. This move- 

 ment withdraws the margin of the globule from 

 the iron and the globule flattens again, which 



