OHM ON THE GALVANIC CIRCUIT. 423 



change, by each variation originating either in the magnitude of 

 a tension or in the reduced length of a part, which latter is itself 

 again determined, both by the actual length of the part, as 

 well as by its conductibility and by its section. This variety of 

 change may be Umited, by supposing only one of the enu- 

 merated elements to be variable, and all the remainder con- 

 stant. We thus arrive at distinct forms of the general equa- 

 tion corresponding to each particular instance of the general 

 capabihty of change of a cu'cuit. To render the meaning of 

 this phrase evident by an example, I will suppose that in the 

 circuit only the actual length of a single part is subjected to 

 a continual change ; but that all the other values denoting the 

 magnitude of the current remain constantly the same, and, 

 consequently, also in its equation. If we designate by x this 

 variable length, and the conductibility corresponding to the 

 same part by x, its section by co, and the sum of the reduced 



lengths of all the others by A, so that L = A H , then the 



general expression for the current changes into the following : 



S= ^— ; 



A+-^ 



X . 0) 



or if we multiply both the numerator and denominator by x w, 

 and substitute a for x w A, and h for x co A, into the following : 



b -f- x"" 



where a and h represent two constant magnitudes, and x the 

 variable length of a portion of the circuit fully determined with 

 respect to its substance and its section. This form of the 

 general equation, in which all the invariable elements have 

 been reduced to the smallest number of constants, is that 

 which I had practically deduced from experiments to which 

 the theor)'^ here developed owes its origin*. The law which it 

 expresses relative to the length of conductors, differs essentially 

 from that which Davy formerly, and Becquerel more recently, 

 were led to by experiments ; it also diiFers very considerably 

 from that advanced by Barlow, as well as from that which I 

 had previously drawn from other experiments, although the 

 two latter come much nearer to the truth. The first, in fact, 



• See Schweigger's Jahrbuch, 1826. Part 2. 



