424 OHM ON THE GALVANIC CIRCUIT. 



is nothing more than a formula of interpolation, which is valid 

 only for a relatively very short vai'iable part of the entire cir- 

 cuit, and, nevertheless, is still applicable in very different 

 possible modes of conduction, which is already evident, from 

 its merely admitting the variable portion of the circuit, and 

 leaving out of consideration all the other part ; but all partake 

 in common of this evil, that they have admitted a foreign 

 source of variability, produced by the chemical change of the 

 fluid portion of the circuit, of which I shall speak more fully 

 hereafter. I have already treated, in other places, more at 

 length of the relations of the various forms of the law to one 

 another. 



From the numerous separate peculiarities of the galvanic 

 circuit resulting from the general equation 



I will here merely mention a few. It is immediately evident 

 that a change in the arrangement of the parts has no influ-g 

 ence on the magnitude of the current if the sum of the ten- 

 sions be not affected by it. Nor is the magnitude of the cur- 

 rent altered, when the sum of the tensions, and the entire reduced 

 length of the circuit, change in the same proportion ; conse- 

 quently a circuit, the sum of whose tensions is very small in 

 comparison to that of another circuit, may still produce a cur- 

 rent, which, in energy, may be equal to that in the other cir- 

 cuit, when merely that which it loses in force of tensions 

 is replaced by a shortening of its reduced length. In this 

 circumstance is the source of the peculiar difference between 

 thermo- and hydro-circuits. In the former only metals occur 

 as parts of the circuit ; in the latter, besides the metals, aqueous 

 fluids, whose power of conduction, in comparison to that 

 of the metals, is exceedingly small; on which account the 

 reduced lengths of the fluid surpass, beyond all proportion, 

 those of the metallic parts, with in all respects equal dimen- 

 sions, and even remain considerably greater when diminished 

 by shortening their actual lengths, and increasing their sec- 

 tions, so long, at least, as this diminution is not carried too 

 far. And thence it is that the reduced length of the ther- 

 mo-circuit is, in general, far smaller than that of the hydro- 

 circuit, whence we may infer a tension smaller in the same pro- " 

 portion in the former, although the magnitude of the current, 



