the acid solution be not very feeble; and these energies seem to improve with an increase of acid in that portion of the fluid.

These electrical relations of the two pieces appear to be constant with every power of the acid solution, even from the first immersion, which is a peculiarity in this experiment that I have not observed, either with copper or zinc, for when those metals are separately employed with nitric acid, of different degrees of strength, the piece which is immersed in the stronger solution first displays its electricity in the character of zinc in the standard battery, and afterwards changes to that of copper, which is not the case with two pieces of iron, for they uniformly display the same electrical relations from the beginning to the end of the experiment.

48. When one piece of iron has been exposed for a short time to the action of a feeble solution of nitric acid, it will operate as zinc to another bright piece which is plunged in afterwards; the latter operating in the character of copper in the standard battery; but this species of action with iron is of very short duration, and the needle almost immediately returns to that direction which marks the last piece immersed to be operating as zinc in the standard battery.

49. Iron and nitrous acid.—The electrical relations of two pieces of polished iron when placed in two portions of this acid, very diffe

oxidized, and liberating gas at its surface, the experiment is not so decisively opposed to the chemical theory of galvanism as when either muriatic or sulphuric acid is employed.

Two pieces of rolled zinc, each presenting ten square inches of surface, one of which was amalgamated, and made quite brilliant, were formed into a galvanic combination with nitrous acid diluted with twelve times its quantity of water, and connected with the galvanometer; the needle after several oscillations reposed at an angle of 65 degrees, after which the following results were observed, without in the least disturbing the apparatus:

The metals were not disturbed for fifteen hours afterwards, at the end of which time the needle marked an angle of 18 degrees. An interruption was now made in the circuit without disturbing the metallic plates; when the needle had reposed in the magnetic meridian the circuit was again completed, and the needle deflected to an angle of 30 degrees, and became steady at 19 degrees.

The electrical powers displayed by two pieces of zinc, the one pure, and the other amalgamated, and a solution of nitrous acid, are sufficiently energetic to produce electro-magnetic rotations, even on a pretty large scale.

rently diluted, or the one piece in the acid solution, and the other in water, are precisely of the same character as when the nitric is employed, but the electrical energies displayed are more energetic. I have experimented with the acid and water in a variety of proportions, and the results are uniformly of the same character; the piece which is placed in the acid solution operates as copper, whilst that in the water, whether acidulated or not, displays the electrical character of zinc in the standard battery.

50. When both pieces are placed in the same acid solution, one a minute or two before the other, the latter, if bright, operates as copper in the standard battery very powerfully indeed; and this singular phenomenon is exhibited to as great an advantage with these materials as with any that I have noticed: but these electrical relations very soon cease, and the pieces almost immediately display electricity in the opposite way, precisely the same as when nitric acid is employed.

51. There is another phenomenon exhibited in these experiments which I believe has never before been noticed, but which, by the regularity of its display, must necessarily involve some theoretical principle, and consequently becomes as interesting to the philosopher as any other; I have observed it more or less in several other experiments, but as it is very decidedly exhibited with these materials I will describe it in this place.

52. When two pieces of polished iron have been for a few minutes immersed in a weak solution of nitrous acid, and in connexion with the galvanometer; if one piece be taken out, and very soon returned to its place, the needle will be deflected to a considerable angle, amounting in some instances to 90°, indicating the piece last plunged in to be operating as copper in the standard battery, and the needle will not return so quickly as if that piece had been bright before immersion, but will frequently retain that character for some time; it takes place with either piece, it is a matter of no consequence which is first plunged into the acid solution; the last will always display the phenomenon I have mentioned. I have obtained the same result for twenty successive times, by first taking out one piece, then the other, leaving them in the solution about half a minute between each time.

53. Iron and muriatic acid.—When two equal pieces of iron are immersed in a solution of muriatic acid, the piece last plunged in will display its electricity in the character of copper in the standard battery. If now, the other piece be taken out, it will also operate in the same capacity, in precisely the same manner as when iron and nitrous acid are employed; and this species of action takes place when the pieces are immersed, the one in the acid solution, and the other in water, so that the first effect indicated by the needle, will depend on the order of immersion; but if they be left unmolested for a minute or two, the piece in the acid solution will operate as copper, whilst that which is surrounded by water will operate as zinc in the standard battery;

and these electrical relations of the two pieces will be uniformly displayed while undisturbed in their respective chambers, but if either piece be in the least moved in the fluid, that piece will immediately operate as copper in the standard battery.

54. This singular and curious phenomenon, which I believe has not before been noticed, I shall endeavour to describe with some degree of minuteness; and likewise the process by which it appears to be the most decidedly exhibited.

Let two flat pieces of good iron, having each about two square inches of surface, exactly alike, and well polished, be connected with the galvanometer, and placed in a vessel containing muriatic acid diluted with two or three times its quantity of water. The needle will vibrate a little, but will soon come to rest; but, as it is next to impossible to select two pieces of iron so nearly alike in their electrical characters as not to display some galvanic effect, it is likely that the needle will not repose in the magnetic meridian, but will make some small angle therewith. Let that piece only, which the needle indicates to be operating as zinc in the standard battery be gently moved in the interposed fluid; the needle will immediately be deflected the contrary way, showing that the electrical relations of the two pieces of metal become changed by this process. When the needle has again come to rest, move the other piece, letting the first moved piece remain unmolested; the needle will again change its direction, and will indicate the last moved piece to be operating as copper in the standard battery.

55. If, whilst the connexions are complete, one of the pieces be moved rapidly to and fro in the acid solution, whilst the other remains at rest, the needle will be deflected to an angle of 40° or 50°, and may be kept steady at about 20° by continuing the motion, still indicating the moving piece to be operating as copper in the standard battery. But the moment the motion has ceased, the needle returns to the meridian, and very frequently takes a position on the other side. 56. I have tried iron with solutions of other acids, but cannot discover that decided effect as with the muriatic. I have also tried if the same phenomenon could be exhibited by employing other metals, such as copper, zinc, brass, &c., in different acid solutions, but I have failed to obtain any thing like that precision of results as are afforded by iron and diluted muriatic acid. In some cases indeed, the same process appears to operate in the contrary way; and particularly with tin in a solution of nitro-muriatic acid, as will be more particularly noticed in the sequel.

57. Iron and sulphuric acid.—I shall have very little to advance under this head, as the phenomena displayed are precisely of the same character as when muriatic acid is employed. There is not however that decided effect produced by agitating one of the pieces, as in a solution of muritic acid, but the result by that process is of the same nature.

From a retrospection of this complicated experiment, it will be observed that the results which I have obtained are very different from those stated in Mr. Ritchie's memoir. Perhaps some of those differences may have emanated from a dissimilitude in the mode of experimenting, or from that gentleman not having noticed those peculiar phenomena which I have minutely described; but there are certainly some discrepancies which I am persuaded no allowance of that nature can possibly reconcile.*

[We believe that the same pamphlet has some claims to priority of making known a few other facts, quite as interesting in these matters as those before alluded to. For instance, the non-necessity of metallic contact in voltaic pairs, and the superiority of rolled zinc over cast zinc, were first made known by that pamphlet.]

I do not, however, suppose with Volta, that the electricity developed by simple contact of the metals, exercises the extent of influence in galvanic arrangements which that philosopher imagined. I have interposed in various ways, pairs of copper and zinc, of two square feet in surface, in the galvanic circle, without observing the least effect in modifying the energies displayed by a pair of wires of the same metals, which were placed in an acid solution. And I have proved by experiments, which will be described in the sequel, that electro-magnetic powers may be displayed without any metallic contact whatever.

[So much for non-metallic contact. Now let us see what the pamphlet says about rolled and cast zinc :-]

68. Two pieces of zinc, each exposing two square inches of surface, the one cast and quite hard and brittle; the other rolled, but sufficiently soft and pliable to wrap round the figure like a strip of sheet lead, were placed in a glass vessel, and connected with the

There is an advantage in separating the two portions of fluid by a bladder partition, which is not afforded by placing the two pieces of metal in separate vessels connected by moistened asbestos, as was the practice with Sir H. Davy; for it is a well known fact, that the nearer the metals approximate each other in the interposed fluid, the greater is the galvanic effect; and when the electrical energies are very feeble, it is necessary to give every facility to the display of the phenomena; hence it will be found, that when both pieces press gently against the opposite sides of the bladder, the needle will be deflected to a greater angle than when they are placed at a greater distance from each other. If unacidulated water be employed in one of the chambers, this precaution will be necessary to be attended to.

This circumstance alone, appears to me highly favourable to the opinion that, the energies of a galvanic combination are exalted in some proportion as the conducting power of the fluid medium becomes improved; for, by shortening the distance between the two plates in the acid solution, a portion of impeding obstacles to the transmission of electricity becomes removed, and the electric stream flows more copiously and with greater celerity by the facility thus afforded, which in fact, amounts precisely to the same thing, as if the distance were constant, and the conductability of the acid solution improved.

galvanometer by proper conducting wires; sulphuric acid was poured in, and a small deviation of the needle was observed, indicating the rolled piece to be operating as zinc in the standard battery. Water, to the amount of about three times the quantity of acid was now gently poured in; the chemical action became excessive, and the needle was deflected 30° in the same direction as at first. The following were the results of five minutes, which was the whole time that the pieces remained in the acid solution :—

69. The metals being now brushed in clean water, were again introduced into the same acid solution. The same electrical relations of the two pieces were again displayed for five minutes, the angle of deflection being steady at 12°.

70. The same pieces were again brushed in clean water, and the experiment repeated with a fresh portion of sulphuric acid, diluted with three times its quantity of water; the metals were connected with the galvanometer, and the results again observed for five minutes, which were as follow:

In experiments with these materials the chemical action is excessively intense for the first three minutes, about which time it generally subsides very rapidly.

The electrical energies appear to diminish from three causes. 1st.-As the chemical action subsides the height of the fluid medium subsides also, and therefore a less portion of metallic surface is exposed in the latter than in the former part of the experiment. 2nd.-The longer the pieces of zinc are exposed to the action of the acid, the more equal they become in the asperous character of their surfaces; consequently, their electrical energies are the most vigourous when the rolled piece is quite new and smooth, or well hammered to level the asperities on the surface-which experience demonstrates. 3rd.-Since by the first part of the experiment, decomposition is rapidly produced, a portion of the constituent parts of the fluid medium becomes either determined in the circuit, or entirely expelled: the latter part therefore, proceeds under very different circumstances, both as regards quality, quantity, and arrangement of the elements employed. This latter cause is common to all galvanic arrangements.