Measure of the relative Tension or Electric Currents. 347 



The following table will at the same time establish Lenz's 

 law in the case of thermo-electric currents, and prove that 

 even in cases where the tension is so exceedingly low, the 

 elastic force of a given quantity of electricity follows the above- 

 named law. 



Table L. 



The current here experimented with was generated by a 

 pair of wires of copper and tinned iron y^^ inch in diameter, 

 and one foot long, the soldered extremity being imnjersed in 

 a bath of boiling water, and the free extremity carefully main- 

 tained at 59^ Fahr. ; the third column in the table being cal- 

 culated by the aid of the constant 1527. 



As respects electricity of high tension, a law extremely ana- 

 logous to that here indicated may be traced. The striking di- 

 stance varies directly as the quantity accumulates. If a given 

 jar be successively charged with quantities of electricity, as 

 the numbers 1, 2, 3, 4, &c., the intervals of air through which 

 the spark can pass, vary directly as those numbers. This is 

 abundantly shown by the experiments of Lane, Harris, and 

 other philosophers. 



Now upon what does this striking distance depend? Plainly 

 upon the elastic force of the coerced fluid, and therefore the 

 striking distance will measure the elastic force or tension. 

 We condense upon a given surface increasing quantities of 

 the electric fluid, and find that the law in relation to its elastic 

 force, is that the tension of a given quantity is inversely as its 

 volume. But this is the law of Marriotte in relation to the 

 ponderable elastic fluids. 



The following numerical determinations were made by 

 adding successive plates to the first single hydro-pair, and 

 taking the values of the current on each addition. It is of- 

 fered merely as an illustration of the chief fact under dis- 

 cussion, and is not to be regarded as absolutely correct, 

 though every precaution was taken to avoid changes in the 

 current. It shows the decrease of quantity and the increase 

 of tension in Volta's instrument. Of course, in reasoning 



