38 THE EFFECT VARIES WITH VARIATION OF ELECTRIC DISTURBANCE. 



other words, if two solids which adhere to a certain fluid, with forces differing iu 

 amount, develop upon rupture quantities of electricity in the same ratio. As a general 

 result, the balance and electrometer prove that this is the case. Bees' wax, which ad- 

 heres to mercury with much less force than gum lac, develops likewise much less 

 electricity. Gum lac, which adheres less strongly than glass, likewise develops much 

 less electricity ; but when we attempt to run a comparison in this manner among a 

 series of substances, we find there are many disturbing causes which, in most cases, in- 

 capacitate us entirely from making comparable results. Much depends on the relative 

 conducting power of the surface employed. A plate of iron may be separated from a 

 surface of mercury, which does not wet it, with a very small disturbance of electric 

 equilibrium, arising from the high conducting power of the metallic plate, which enables 

 a transfer of any free electricity to take place if the plate should tilt on one side, or any- 

 thing affect its horizontality during the act of separation. In proportion as the con- 

 ducting power increases, although the force of adhesion may remain the same, the total 

 effect on the electrometer should diminish ; and this is agreeable to experience. Again, 

 the presence of moisture on any part of the touching surfaces will vitiate the results ; 

 partly owing to its high conducting power, but chiefly to the circumstance that it hin- 

 ders the surfaces under trial from ever coming into contact. 



122. The circumstance of this great variability in the amount of developed electricity 

 is in itself strong evidence of relationship between the supposed cause and the effect. 

 Gay-Lussac found that it required a weight, sometimes of 158, and sometimes of 296 

 grammes, to detach a certain disk of glass from mercury, depending on causes which 

 were not very apparent. An effect thus differing in amount indicates a cause of like 

 variability, or subject to many disturbances. 



123. I regard, therefore, the agent bringing about capillary phenomena as identical 

 with that producing chemical action, and both as being due to electricity. The force 

 of cohesion bears the same relation to both, acting on both as a disturbing power. 

 Nay, we may even take a much more extensive view of the matter, and from the ratio 

 these forces bear to each other predicate the effect of their combined action, which may 

 be classed under three distinct heads. 



1st. If the force of attraction of the particles of a solid for the particles of a fluid be 

 not equal to half the cohesive force of the latter for each other, the fluid will refuse to 

 pass through a pore of that solid substance, and in capillary vessels consisting of it will 

 be depressed below its hydrostatic level. 



2d. If the force of electric attraction of the particles of a solid for the particles of a 

 fluid exceeds half the cohesive force of the latter for each other, but is not equal to the 

 whole force, the fluid will pass through a pore formed of that solid substance, and in a 

 capillary tube of it, will rise above its hydrostatic level. 



3d. If the force of electric attraction of the particles of a solid for the particles of a 

 fluid exceed the whole cohesion of the latter, chemical union ensues. 



124. In thus assimilating the force producing pressure on planes and motion in nar- 

 row pipes, with the force producing chemical changes in the constitution of bodies, a 

 great advantage is gained in simplifying physiological investigations in respect of the 



