of Electrical a7id Chemical Changes. 37 



and describe the manner in which I have used the terms which 

 have been adopted in electro-chemical science. 



In determining the nature of the electrical action in what 

 may be called the closed cu'cle, or the combinations in which, 

 according to the language used on the continent, electrical 

 currents exist, I have employed instruments constructed upon 

 the same principles as the galvanometer of Professor Cum-r 

 ming, or the multiplier of Professor Schweigger. Silver wire, 

 covered with silk, about l-70th of an inch in diameter, was 

 folded round a small wooden frame, so as to fill a narrow 

 deep groove : the two extreme wires were parallel, and the 

 convolutions as nearly as possible in the same perpendicular : 

 a small tube containing a filament of silk was passed through 

 the centre of the convolutions of wires, to which a delicate 

 magnetised needle was suspended ; which, when the apparatus 

 was properly disposed, rested with its north pole between the 

 two extremities of the wii'es. This instrument, which con- 

 tained 60 circumvolutions of wire, was found sufficiently de- 

 licate for most purposes of experiment; but in a few instances, 

 in which very weak electricities were to be determined, I 

 used another apparatus, in which the same kind of wire was 

 fastened, in concentric circles, round two portions of glass 

 tube, in such a manner that radii from the inner circle would 

 have passed through all the wires, and in which increased 

 mobility was given to the system by two needles exterior to 

 it and connected with it, placed one above, the other below 

 the central needle, with their poles in the same directions, but 

 opposite to those of the central needle, which was so mag- 

 netised that its directive power was neutralised by the power 

 of the other two needles *. 



To illustrate the operation of these apparatus, I shall state, 

 that when the lower terminating wire, which was to the left, 

 or east of the north pole, was connected with a piece of zinc, 

 and the upper one with a piece of platinum, both beino- in 

 common water, the deviation of the central needle was eight 

 or ten degrees, the south pole turning to the east or left 

 hand; which may be considered as indicating that the current 

 of electricity was from the platinum to the zinc through the 

 wire, and that the surface of the zinc in the fluid was positive 

 with respect to the opposite surface of platmum ; and in usino- 

 the terms positive and negative, I beg to be understood as 

 applying them to the metallic surfaces in contact with the 

 fluid. 



* This arrangement differs from that of M. Nobile only by a duphca- 

 tion of eftbct. 



