LONG-CONTINUED ELECTRIC CURRENTS OF LOW TENSION. 
39 
tity of electricity appearing to be by no means so important as a continuous and equable 
current. For similar reasons Mr. Mullins’s modification of Professor Daniell’s bat- 
tery was found equally objectionable ; added to which the currents evolved are liable 
to be materially affected by the admixture of the exciting fluids through the mem- 
branous partition, which always takes place sooner or later by endosmosmic action. 
4. After several experiments I was induced to prefer the following apparatus, (which 
after all is but a slight modification of Professor Daniell’s,) in consequence of its 
affording a constant and regular current of electricity of very weak tension, con- 
tinuing for several weeks or even longer without any fresh addition of exciting fluid. 
A glass cylinder, T5 inch in diameter and 4 inches in length, was closed at one end 
by means of a plug of plaster of Paris 07 inch in thickness : this cylinder was fixed 
by means of corks inside a cylindrical glass vessel about 8 inches deep and 2 inches 
in diameter. A piece of sheet copper, 6 inches long and 3 inches wide, (having a 
copper conducting wire soldered to it,) was loosely coiled up, and placed in the 
small cylinder with the plaster bottom : a piece of sheet zinc of equal size was also 
loosely coiled up, and placed in the larger external cylinder (being furnished like the 
copper plate with a conducting wire). The larger cylindrical glass being then nearly 
filled with weak brine, and the smaller with a saturated solution of sulphate of copper, 
the two fluids being prevented from mixing by the plaster of Paris diaphragm, the 
apparatus is complete* ; and if care is taken that the fluids in the two cylinders are 
at the same level, will continue to afford a continuous current of electricity for some 
weeks, the sulphate of copper being very slowly decomposed. So feeble is the cur- 
rent evolved by an apparatus of this kind, that on connecting the two conducting 
wires with a common galvanometer, (having but one needle suspended on a pivot,) a 
deviation to only 10° or 12° took place: with Nobili’s galvanometer, with nearly 
astatic needles, a deviation to 90° immediately ensued, as might be expected from 
the greater delicacy of the instrument. So small, indeed, is the quantity of electri- 
city evolved by the apparatus I have described, as compared to that evolved by the 
ordinary electromotor, that I was unable to produce the simplest form of electro- 
magnetic rotation by its aid. After it has been in action for some weeks, chloride of 
zinc is found in the external cylinder, and beautiful crystals of metallic copper, fre- 
quently mixed with the ruby protoxide (closely resembling the native ruby copper 
ore) and large crystals of sulphate of soda, are found adhering to the copper plate in 
the smaller cylinder, especially on that part where it touches the plaster diaphragm. 
* So simple an apparatus scarcely requires an illustration : in the accompanying outline sketch I have, how- 
ever, figured it, to prevent any error arising from the account in the next not being sufficiently explicit. 
Fig 1. represents the battery connected with the apparatus described in paragraph 4. 
A. The external cylinder. 
B. The smaller one ; with D. The plaster of Paris bottom. 
C. The coil of copper in the cylinder B, having the conducting wire F soldered to it. 
E. The coil of zinc with the wire G soldered to it. 
