492 M. PoggendorfF on Gahanic Circuits composed of 



drying with bibulous paper, or, if it seemed requisite, by rub- 

 bing with sand-paper, scouring with sand and acids or M^ater ; 

 although these operations are exceedingly troublesome from 

 frequent repetition, yet they were never neglected. Moreover, 

 the platina was, previous to each experiment, heated over an 

 alcohol lamp after having been cleansed, as it otherwise only 

 produces weak effects. I therefore believe that the following 

 results merit some confidence, especially as most of them are 

 deduced from several experiments repeated on various days. 



Before, however, communicating these results, I must still 

 add one remark. 



By whatever cause the electricity may be produced in cir- 

 cuits of this kind, it is evident that there can be no doubt 

 respecting the ivhere, that it can only occur at the places of 

 contact of the fluids with the metals, — since a contact of hete- 

 rogeneous metals does not take place, or rather each of the two 

 metallic slips contains two such contacts, which, from their 

 being of opposite nature, must necessarily nullify each other. 

 There are, therefore, in this kind of circuits four possible places 

 of excitation, two in each vessel ; and if we combine the electro- 

 motive force developed in each vessel, we have two such forces, 

 e and e', M'hich act in opposition to each other. If, moreover, 

 we call r the total resistance of the circuit, then, according to 

 Ohm^s fundamental law for the intensity of the resulting cur- 



6 — e' 

 rent, we obtain the expression . 



Accordingly, the direction of the current, i. e. the direction of 

 the deflection of the needle of the multiplier, depends solely on 

 the sign of the difference e — e' ; on the other hand, the inten- 

 sity of the current, or the magnitude of the deflection, both on 

 the value of the difference e — e' and on the value r of the 

 resistance. The amount of the deflection of the needle affords 



gen, the temporarily negative one, so it seemed, always to a greater extent ; yet 

 but few bubbles ascended from it. 



Amalgamated plates exhibit the same phasnomena; but since in this case 

 stronger acid may be employed without giving rise to any disturbance, it can 

 be observed that the mere raising one of the plates about one inch renders 

 it considerably negative ; re-immersion again increases the negativeness. I 

 observed this with sulphuric acid of 1-827 spec. gr. diluted with 9 times its 

 volume of water, into which the plates were immersed to the depth of 2-5 inch. 



These enigmatical currents are all of them, however, but of transitory 

 duration, and they can therefore, in the following experiments, in which 

 the positive metal, situated in the acid, was in most cases immersed last, at the 

 utmost have only effected the first deflections, and then only when these were 

 feeble. But in general the heterogeneity which originates for the positive 

 plates from the contact with two fluids, is far stronger. At times I have 

 also convinced myself that the results were essentially the same, whether the 

 positive plates were immersed at the same timcj or one after the other, before 

 or after the negative plates. 



