GENERAL LAW. 



87 



far as I am informed, the magnetic spark and the true thermo-electric spark have never 

 yet been seen. 



316. These observations are made in order that I may not be misunderstood. It 

 is not my object to consider the different arrangements that can generate a Faradian 

 current, and, therefore, in this point of view I dismiss the flat spiral. 



317. We now come to the fourth and last proposition, which is, " That the law 

 which regulates the connexion of the diminution of quantity or condensation with the 

 increase of tension, is the same as that which regulates the analogous phenomena of 

 ponderable elastic fluids." 



318. I have not hesitated to use the terms " compression," " condensation," " elastic 

 force," in reference to electricity, though I well know such an application is unusual. 

 But it has seemed to me that a single pair might almost be likened to a steam-engine 

 boiler, from which if you let the steam escape by a wide tube, its elastic force is less 

 and less, accordingly as the escape is more free ; but, if you put upon it a narrow tube, 

 the vapour rushes with vehemence through it, reaction in a moment occurs in the 

 boiler, the elastic force increases, and the accumulated steam pressing heavily on its 

 surface, the water boils in a more laboured way : this narrow tube resembles HENRY'S 

 coil, or a long or slender wire. 



319. The following table exhibits numerical results obtained by the aid of one of 

 DANIELL'S constant batteries, the tension being continually increased by the addition of 

 successively increasing lengths of wire 



TABLE K. 



320. From this table it would appear that the addition of successively increasing 

 lengths of wire of invariable diameter diminishes the absolute quantity of electricity 

 flowing, but at the same time the tension is exalted. By taking the angle of torsion as 

 the measure of the forces, in the second column, it is also evident that the law of the 

 conducting power of wires given by M. LENZ holds in the case of a hydro-electric pair. 

 This may be regarded as of some interest, inasmuch as the late Dr. RITCHIE, in certain 

 papers read before the Royal Society, opposed to the very last this view, by the aid 

 of numerical determinations made with the torsion balance, the instrument here em- 

 ployed. In reference to the third column of the table, I have calculated it in the man- 

 ner given by LENZ, the value of the constant to be deduced from the reciprocals of the 

 angles of torsion being in this case 1318 nearly. 



321. While, therefore, these results confirm, in the most pointed manner, the reason- 

 ing of that able philosopher, they at the same time compel us to advance a step far- 



