426 OHM ON THE GALVANIC CIRCUIT. 



portion. Consequently, if merely such circuits are compared 

 in which the fluid parts have the same actual lengths and the 

 same conductibilities, then the magnitude of the current in these 

 circuits is in direct ratio to the section of the fluid portio7i. 

 However, it must not be overlooked, that a more complex defi- 

 nition must take the place of this simple one when the reduced 

 length of the metallic portion can no longer be regarded as 

 evanescent towai-ds that of the fluid, which case occurs when- 

 ever the metallic portion is very long and thin, or the fluid 

 portion is a good conductor, and with unusually large terminal 

 surfaces. 



From the equation 



^- L 



we can easily perceive that, when a portion is taken from the 

 galvanic circuit, and is replaced by another, and after this 

 change the sum of the tensions as well as the energy of the 

 current still remains perfectly the same, these two parts have 

 the same reduced length, consequently their actual lengths are 

 as the products of their conductibilities and sections. The actual 

 lengths of such parts are therefore, when they have like sections, 

 as their conductibilities, and when they have like conductibilities 

 as their sections. By the first of these two relations we are 

 enabled to determine the conductibilities of various bodies in 

 a far more advantageous manner than by the pre\-iously men- 

 tioned process, and it has already been employed by Bec- 

 querel and myself for several metals*. The second relation may 

 serve to demonstrate experimentally the independence of the 

 effect on the form of the section, as has previously been done 

 by Davy, and recently by myselff. 



In the voltaic pile, the sum of the tensions, and the reduced 

 length of the simple circuit, is repeated as frequently as the 

 number of elements of which it consists expresses. If, there- 

 fore, we designate by A the sum of all the tensions in the simple 

 circuit, by L its reduced length, and by 7i the number of ele- 

 ments in the pile, the magnitude of the current in the closed 

 pile is evidently 



* Bulletin uiiivjrsel. Physique, Mai 1825, and Schweigger's Jahrbuch, 

 1826. Part 2. 

 t Gilbert's Annalen, nn. Folge. Vol. xi. p. 253, and Schweigger's Jahrbuch, 



1827. 



