OHM ON THE GALVANIC CIRCUIT. 425 



in the thermo-circuit, cedes in nothing to that in the hydro- 

 circuit. The great difference between a thermo- and hydro-cir- 

 cuit, both of which produce a current of the same energy, is evident 

 when the same change is made on both, as ivill be shown in thefoU 

 lowing consideration. Let the reduced length of a thermo- 

 circuit be h, and the sum of its tensions A, the reduced length 

 of an hydro-circuit m L, and the sum of its tensions m A, 

 then the magnitude of the current in the former is expressed by 



A 771 A. • 



-^, in the latter by — ^, and is consequently the same m 

 L '' m L, 



both circuits. But this equality of the current no longer 

 exists if the same new part X of the reduced length be intro- 

 duced into both, for then the magnitude of the cun-ent is in 

 the first 



A 



in the second 



L + X' 



m A 



m L + x" 



If we connect with this determination an evaluation, even if 

 merely superficial, of the quantities m, L, and \, we shall readily 

 be convinced that in cases where the simple hydro-circuit can 

 stiU produce in the part A actions of heat or chemical decompo- 

 sition, the simple thermo-circuit may not possess the hundredth, 

 and in some cases not the thousandth part of the requisite force, 

 whence the absence of similar effects in it is easily to be under- 

 stood. We are also able to understand why a diminution of the 

 reduced lengths of the thermo-circuit (by increasing, for instance, 

 the section of the metals constituting it) cannot give rise to the 

 production of those effects, although the magnitude of its 

 current may be increased by this means to a higher degree than 

 in the hydro-circuit producing such effects. This difference in 

 the conductibihty of metallic bodies and aqueous fluids, is the 

 cause of a peculiarity noticed with respect to hydro-circuits, 

 which it is here, perhaps, the proper place to mention. Under 

 the usual circumstances, the reduced length of the fluid 

 portion is so large, in comparison to that of the metallic portion, 

 that the latter may be overlooked, and the former alone taken in- 

 stead of the reduced length of the entire circuit ; but then the 

 magnitude of the current in circuits which have the same ten- 

 ! sion is in the inverse ratio to the reduced length of the fluid 



Vr)|,. 11. PART VII. 2 F 



