Measure of the relative Tension of Electric Currents. 3 45 



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 tree; 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 resem- 

 bles Henry's coil, or a long or slender wire. 



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. 



From this table it would appear, that the addition of suc- 

 cessively increasing lengths of wire of invariable diameter, di- 

 minishes 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, in as much as the 

 late Dr. Ritchie, in certain papers read before the Royal So- 

 ciety*, opposed to the very last this view, by the aid of nume- 

 rical determinations made with the torsion balance, the in- 

 strument here employed. In reference to the third column 

 of the table, I have calculated it in the manner given by 

 Lenz, the value of the constant to be deduced from the reci- 

 procals of the angles of torsion being in this case 1318 nearK'. 



Whilst therefore these results confirm in the most pointed 

 manner the reasoning of that able philosopher, they at the 

 same time compel us to advance a step further, and to expand 



[* L. & E. Phil. Mag., vol. xi. p. 192. Edit.] 



