348 Dr. Draper on the Tension of Electric Currents. 



upon it, the hypothetical action of each plate is assumed to be 

 equal to that of any other in the series. 



Table M. 



Thermo-electric piles are well known to give the same 

 general results, as respects tension, that hydro-electric piles 

 do : they are much better suited to the purpose of the experi- 

 menter, and give currents that are far more constant. The 

 following table represents the action of such a battery, con- 

 sisting of wires of copper and tinned iron, each element being 

 about one foot long and -^^ inch in diameter. The source of 

 heat was a bath of boiling water. 



Table N. 



The beautiful experiments of Becquerel, and the equally 

 elegant repetition of them by Dr. Golding Bird, show that 

 the view I have here taken of the action of a single pair is 

 correct. The latter chemist found, that not only could a 

 single pair decompose bodies, such as iodide of potassium, 

 &c., which easily yield up their elements, but that the am- 

 moniacal amalgam might be formed, potassium reduced, and 

 in point of fact any decomposition effected. And what is 

 the plan followed ? The current is forced to pass, in the elec- 

 trolyte that is to be decomposed, an obstacle or resisting me- 

 dium; the tension instantly rises, but at a vast sacrifice of 

 quantity, so that the magnetic needle, which measures only 

 the quantity passing in an indivisible portion of time, is barely 

 affected. Yet, by continuing the current for a great length 

 of time, the resulting decomposing effects are finally the same 

 as those obtained more speedily by the action of many pairs. 



