OHM ON THE GALVANIC CIRCUIT. 473 



point of excitation, is known, and is equal to b, which case 

 always occurs when the electroscopic force of the circuit is 

 given at any one of its places, we obtain 



and after substitution and proper reduction, 



which for Z» = 0, i. e. for a circuit left entirely to itself, changes 

 into 



These equations, which hold for a circuit homogeneous and pris- 

 matic in its whole extent, change when /3 = again into the above, 

 where the influence of the atmosphere on the circuit was, under 

 the circumstances given above, left out of consideration. Since 



be. 

 /3^ = — . — , it follows that the influence of the atmosphere on 



the galvanic circuit must be less, the smaller the conducting 

 power of the atmosphere is in comparison to that of the circuit, 



c , c 



and the smaller the quotient — is. But the quotient — ex- 

 presses the relation of the surface of a disc of the conductor 

 surrounded by the atmosphere to the volume of the same disc, 



c 

 and it might therefore appear that — must constantly be in- 

 to 



finitely small. However, it must not be forgotten that we 

 have not here to deal with mathematical, but with physical de- 

 terminations ; for, strictly taken, c does not represent a surface, 

 but that portion of a disc of the circuit on which the atmosphere 

 has direct influence, and w in fact signifies nothing more than 

 that part of a disc of the cii'cuit which is traversed by the elec- 

 tricity continually passing through the circuit. In general, 

 therefore, c is indeed incomparably smaller than w ; but where 

 the electric current can only move forwards with the greatest 

 difficulty, and on that account but very slowly, as is more or 

 less the case in dry piles, the magnitude c may, in accordance 

 with what was stated in the preceding paragraph, become 

 very nearly equal to « ; for undoubtedly a gradual transition. 



