2 Professor Reicli on the Electrical Currents 



let out till it readied to the second point of contact, near 

 which the multiplicator was placed, and the two ends of the 

 fine wires connected with it. The mvdtiplicator, with double 

 needle, and very sensible, belonged to a tliermo-electi-ic appa- 

 ratus of Melloni, made by Oertling of Berlin. In order, in 

 some measm-e, to judge of its sensibility, it maybe mentioned, 

 that the current from a pair of zinc and copper plates, of only 

 one inch square, placed in water very weakly acidified, drove 

 the needle up to the button placed at 90° to prevent further 

 deviation ; that an iron-wire connected with two brass-wires 

 placed in the multiplicator, by the mere heating with the hand 

 of the point of contact, produced a deviation of from 10° to 

 20^, according to the temperatm'e communicated. 



When a deA'iation took place, I tried each time the direction 

 of the current by means of a zinc-copper element, separated 

 by a layer of moistened cloth, and set it down as it was in the 

 long wire of connection. When, therefore, it is said the cur- 

 rent is from A towards B, that is as much as to say that at A 

 was a copper, and at B a zinc plate, and the rock or country 

 intervening was a moist conductor. In this country itself 

 we have, of course, to imagine the current in the opposite di- 

 rection. 



Frequently, also, when no action on the multiplicator en- 

 sued, I introduced a zinc-copper element, so that the current 

 must necessarily pass along the wire between the two points of 

 contact. If an action ensued, it was a proof that every thing- 

 was in order, that is, that the contact was nowhere interrupted. 

 This experiment is always to be recommended, but especially 

 where no action ensues, in order to have proof that the excep- 

 tion is not the consequence of an interruption in the continuity 

 of the wire, nor cf an imperfect contact of the plates with the 

 Avire, or with the mineral mass, nor of a deficiency in the ad- 

 justment of the multiplicatoi", nor of any such similar cause. 

 In fact, it once occurred to me, that two points from which, 

 according to previous experiments, an action was expected, in- 

 duced none. It very soon appeared, however, that the wire 

 was broken, and, on its being reunited, the action took place. 

 Some modifications in the method of conducting the experi- 

 ments will be mentioned, as opportunity presents itself. 



