FAEADAY'S CONCEPTION OF ELECTRICITY. 247 



rapidly through the oil of turpentine than if you take it away and fill 

 the cell only with air. 



Also in this case we may observe polarization of the electrodes as a 

 symptom of previous electrolysis. Another sign of electrolytic con- 

 duction is, that liquids brought between two different metals produce 

 an electro-motive force. This is never done by metals of equal tem- 

 perature, or other conductors which, like metals, let electricity pass 

 without being decomposed. 



The same effect is also observed even with a great many rigid 

 bodies, although we have very few solid bodies which allow us to 

 observe this electrolytic conduction with the galvanometer, and even 

 these only at temperatures near to their melting-point. It is nearly 

 impossible to shelter the quadrants of a delicate electrometer against 

 being charged by the insulating bodies by which they are supported. 



In all the cases which I have quoted one might suspect that traces 

 of humidity absorbed by the substances or adhering to their surface 

 were the electrolytes. I show you, therefore, this little Daniell's cell, 

 in which the porous septum has been substituted by a thin stratum of 

 glass. Externally, all is symmetrical at both poles ; there is nothing 

 in contact with the air but a closed surface of glass, through which 

 two wires of platinum penetrate. The whole charges the electrometer 

 exactly like a Daniell's cell of very great resistance, and this it would 

 not do if the septum of glass did not behave like an electrolyte. All 

 these facts show that electrolytic conduction is not at all limited to 

 solutions of acids or salts. 



Hitherto we have studied the motions of ponderable matter, as 

 well as of electricity, going on in an electrolyte. Let us study now 

 the forces which are able to produce these motions. It has always 

 appeared somewhat startling to everybody who knows the mighty 

 power of chemical forces, the enormous quantity of heat and of me- 

 chanical work which they are able to produce, and who compares with 

 it the exceedingly small electric attraction which the poles of a battery 

 of two Daniell's cells show. Nevertheless, this little apparatus is able 

 to decompose water. 



The quantity of electricity which can be conveyed by a very small 

 quantity of hydrogen, when measured by its electrostatic forces, is ex- 

 ceedingly great. Faraday saw this, and has endeavored in various ways 

 to give at least an approximate determination. The most powerful 

 batteries of Leyden-jars, discharged through a voltameter, give scarcely 

 any visible traces of gases. At present we can give definite numbers. 

 The result is, that the electricity of one milligramme of water, sepa- 

 rated and communicated to two balls one kilometre distant, would 

 produce an attraction between them equal to the weight of twenty- 

 five thousand kilos. 



The total force exerted by the attraction of an electrified body 

 upon another charged with opposite electricity is always proportional 



