Zinc-Iron Circuit, its catises, and some allied subjects. 45 



weakened very easily, and in any degree, by the interposition 

 of a long column of liquid, but they then become unmeasura- 

 ble if the multiplying (multiplicatorischen) means be not in- 

 creased in the same proportion. A multiplier, with 16 to 

 20,000-feet long copper wire, such as employed by Fechner, 

 is an essential requisite for such inquiries. 



On the other hand, it will be perceived that the ascendency 

 of the current of the iron-circuit will sink in that measure more, 

 when we, under otherwise like circumstances, take the plates 

 of both circuits larger, but still remaining equal; but evidently 

 a considerable size of the plates will be requisite to render the 

 current of the copper circuit more powerful, or even as pow- 

 erful as that of the iron circuit. 



And therefore it is that the discovery of Mr. Roberts is of 

 importance in the practical application. With moderate size 

 of plates and moderate resistance, which may already at pre- 

 sent be foreseen, we may in all the usual circuits and piles 

 substitute iron with considerable advantage for copper, both 

 with respect to oeconomy as well as to action ; and the more 

 so in piles or many-membered circuits, as the ascendency 

 of the zinc-iron combination over that of zinc-copper must 

 increase with the number of plates. 



The author, intending subsequently to communicate more 

 accurate measurements on this as well as on allied subjects, 

 is induced, however, to observe, that the iron circuit, al- 

 though not affording a constant current, still possesses, in so 

 far, a not inconsiderable advantage over the copper circuit, 

 as the intensity of the current decreases with it slower than 

 with the latter. 



Lastly, the iron- circuit is therefore of much interest, for 

 the theory, in as far as it perhaps exhibits more distincdy and 

 decidedly than any other known phasnomenon the presence 

 and influence of the resistance to transition still doubted by so 

 many*. There is a whole series of similar phsenomena, espe- 



• Even the autlior was formerly inclined to suspect in the resistance to 

 transition, at least partially, an effect of the disciiarge, which, indeed, ac- 

 tually occurs in many observations not entirely foreign to the above. But 

 experiments made by him on the passage of the currents of Saxton's ma- 

 chine through fluids, in which a discharge in a perceptible degree cannot 

 have place, convinced him subsequently, most decidedly, of the existence 

 of such a resistance. 'J'he first interposition of a thin layer of fluid in the 

 circuit produced a resistance at least four to five times as great as the dou- 

 bling of this layer, as could be observed by means of an air-thermometer, 

 and a peculiar, well-adapted arrangement for the accurate measurement of 

 resistances. That, moreover, the resistance of transition with iron, even 

 in a solution of caustic potash, a liquid which docs not dissolve this metal, 

 is smaller than with copper, evidently proves that this resistance is not 

 always in inverse ratio to tlic clicniical attack, which, indeed, has long 



