391 
electrical and chemical changes. 
tained, 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 circle, 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 
Cumming, or the multiplier of Professor Schweigger. Silver 
wire, covered with silk, about 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 appa- 
ratus was properly disposed, rested with its north pole 
between the two extremities of the wires. This instrument, 
which contained 60 circumvolutions of wire, was found suffi- 
ciently delicate 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 magnetised that its directive power was neu- 
tralised by the power of the other two needles.* 
* This arrangement differs from that of M. Nobile only by a duplication of effect. 
