480 OHM ON THE GALVANIC CIRCUIT. 



the powers of conduction, therefore, of both bodies are directly 

 proportionate to their lengths, and inversely proportionate to their 

 sections. If it is intended to employ this relation in the deter- 

 mination of the powers of conduction of various bodies, and we 

 choose for the experiments prismatic bodies of the same section, 

 which indeed is requisite for the sake of great accuracy, their 

 lengths will enable us to determine accurately their conductibi- 

 lities. 



25. In the preceding paragraph we have deduced the magni- 

 tude of the current from the general equation given in § 18, 



u = -j^y — O + c, 



and have found that it is expressed by -r^, the coefficient of y. 



To ascertain the value f~ ^^ '^^ ^" general requisite to possess 



an accurate knowledge of all the single parts of the circuit, 

 and their reciprocal tensions ; but our general equation indi- 

 cates a means of deducing this value likewise from the nature 

 of any single part of the circuit in the state of action, which 

 we will not disregard, as it will be of great service to us here- 

 after. If, namely, we conceive in the above equation y to be 

 increased by any magnitude A y, and designate by A O the 

 corresponding change of O, and by A m that of u, there results 

 from that equation 



A« = ^A^^ AO, 



and we thence find 



A _ Az<+ AO 

 L - Ay ' 



we find, therefore, the magnitude of the electric current by 

 adding to the difference of the electroscopic forces at any two 

 places of the circuit the sum of all the tensions situated between 

 these two places, and dividing this sum by the reduced length of 

 the part of the circuit which lies between these same places. If 

 there should be no tension within this portion of the circuit, 

 then A O = 0, and we obtain 



A _ Am 



r " A^' ^ 



26. The voltaic pile, which is a combination of several similar 



