electric matter, nor the vector, themselves, but must be contained in them, combined with some other substances, which prevent them from exercising their characteristic effects; a case most common in chemical compounds. The characteristic effect of fire, is heat; when free it acts upon the thermometer; but it does not, when combined with other substances. Lucidity is the characteristic effect of light; but this is not lucul in phosphori, till they are decomposing: and also various bodies, while decomposing emit odorate substances, which in their compound state had no odour. Now, the light emitted by the electric fluid probably belongs to the vector, which has many properties of the former; but it is not lucid, therefore light must be combined in it with some other ingredient. The odorate substance appears to belong to the electric matter, but this has no odour, therefore the former must also be combined in it with some other substance. Lastly, the fire emitted cannot be referred directly to either the vector or the electric matter; but probably, during their common decomposition, it is itself composed of the light and igneous matter disengaged. That fire is a compound, is a system which I have also treated with many experimental details in the above mentioned works.

No natural philosopher, who has applied to the study of any main branch of terrestrial phenomena according to the rules of analysis instituted by the immortal Bacon, will be repulsed by the idea of so many elements entering into the composition of the electric fluid, though hitherto almost excluded from the catalogue of chemical substances by a class of chemists who confine their observations within their laboratories. When, with the view of ascending from some of the most common phenomena to general causes, we have followed this scrupulous analysis by a certain number of regular steps, we are yet, in almost every branch, stopped for want of intelligible links, though in series of phenomena manifestly connected together by some common cause; as for instance many phenomena manifested in our chemical operations, with some which we daily observe in the atmosphere, that great laboratory of nature on our globe. The filling up of these chasms by gratuitous hypotheses is only protracting the attainment of real knowledge.

Let not therefore natural philosophers lose sight of an expansible fluid, constantly associated with all terrestrial bodies, and with the air that surrounds them; this present in all our chemical processes, during which some of its ingredients, either engaged or disengaged, might account really for certain phenomena hitherto explained by mere words. For, according to meteorological observations which I shall relate in the following paper, it is by its decompositions, alternating with compositions, that the electric fluid operates in terrestrial phenomena. What were chemical theories before the chemical combinations of fire with other substances were discovered and attended to? However, as long as this fluid shall be considered under the vague idea expressed by the modern word caloric, it will not much forward the science of chemistry.

After these general remarks, I return to my subject, which will serve as an example of their application. When the transmission of the electric fluid through interrupted conductors takes place in a liquid, the new phenomena of lucidity, heat, and odour, are not perceived; but there cannot be any doubt, that the chemical effects produced in the circuit, and the shock, proceed from the same decomposition of particles, that takes place at interrupted conductors, which is visible only through the air; for no chemical effect is produced in the water of the glass tubes, when the metallic wire passes through it uninterrupted. With respect to the shock, this condition is not immediately perceived in the discharge of the Leyden vial, because it is sudden, attended with a strong commotion, and not repeated till the vial is again charged; but with the pile, which soon renews spontaneously the cause of the shock, it has been seen in Exp. 8, that this phenomenon is produced only at the approaching contact, and thus by an interruption; since all sensation ceased when I fixed the silver spoons on both extremities.

These preliminary deductions of facts were necessary for the solution of the first of the questions above stated, namely: "Of what nature is the modification produced in the electric fluid, when it pervades a pile wherein the calcination of some metal is going on?" A question intimately connected with this: "How does it happen, that, with such a minute quantity of electric fluid set in motion by the pile, the shock and chemical effects are produced, while they require a very great quantity of the same fluid when set in motion by any of the other known apparatuses?" Being arrived at the general fact above stated, that these effects are never produced but by the decomposition of some particles of the electric fluid, occasioned by an excess of density, in darting from one point of a conductor to another, the answer to the connected questions is obvious: the modification undergone by the electric fluid in pervading this pile is such, that some of its particles are decomposed by a very small increase of density, when a conductor is interrupted. We have an analogy of the general case of more easy decomposition of compounds by previous modifications of the latter, in the processes of smelting ores, for obtaining metals or reguli from them; for an easy separation of the ingredient of the latter must be prepared by subtraction or addition of other ingredients, and often by both. And as we see that the calcination by an acid is necessary to produce the shock, it is probable, that the modification of the electric fluid in this case is the addition of some element.

I come now to the second of the above questions: "What is the cause of a motion of the electric fluid in the pile, either producing, or not producing, the shock and chemical effects in the circuit ?" The first point to be considered with respect to this question concerns the nature of the modifications reciprocally produced by zinc and copper upon each other, when brought into contact. It is generally said, that, in this case, ZINC becomes positive, and COPPER negative. But these expressions, according to what has been stated

above, cannot relate to the expansive power of the electric fluid; for, between two bodies in mutual contact, such a power must be in equilibrium; therefore these expressions must relate to density, such as I have defined it. Let us now attend to the experiments.

These trials are usually made with discs of zinc and copper (or brass) having an insulating handle in their centre, like the plate of an electrophorus, and with the help of the condenser; thus, one of the discs being held on the hand, the other is first laid upon it, then brought, by its insulating handle, into contact with the condenser. It is commonly supposed that the latter must be touched while it lies on the other; but this, assimilating the process to that of the electrophorus, changes the nature of the phenomenon, and may lead into error. I shall therefore first relate the experiments which I have made, with discs of the two metals about four inches diameter, from which the difference between these effects will be seen. But I must premise, that in these experiments, the results are very various at different times with respect to the quantity of effect; I shall therefore relate first such experiments as I set down in a certain part of one day; then mention the differences.

Exp. 30. I held the copper plate on my hand, and laid it upon the zinc plate, which I touched with my finger in this situation, and then carried to the condenser: after twenty repetitions of these alternate contacts, the divergence, then positive, of the gold leaves of the latter, was about half an inch.

Exp. 31. I made the same experiment without touching the zinc plate the gold leaves struck the sides. I repeated the same process with only ten alternate contacts, and the same quantity of effect was produced as with twenty, when touching the zinc plate.

I must now mention that at other times I have found no difference of effect from either touching or not touching the zinc disc while lying on the copper disc; and that at different times the quantity of effect in both operations was smaller; a point to which I shall return: but these first experiments prove directly, that when zinc is in communication with copper, the former takes from the latter some electric fluid, making other bodies, on its opposite side, share its excess. Thus, after a certain number of repetitions of the alternate contacts, when the upper plate of the condenser is removed, the fluid accumulated on the receiving plate is manifested by the electroscope : and instead of having increased the effect by touching the zinc on the copper, the finger has sometimes, even during that contact, taken off a part of the accumulated fluid. I come to the reverse experiment, made also at a certain part of one day.

Exp. 32. I took the zinc disc on my hand, and, placing the copper disc on it, I touched the latter before carrying it to the condenser, which it made negative. I repeated the experiment without touching the copper disc lying on the zinc disc, and the negative effect was of the same quantity. In general, a greater number of alternate contacts is required to produce the same quantity of negative effect with copper, than of positive with zinc.

We see however in this experiment the same phenomenon as in the preceding, in this respect, that when zinc and copper are in mutual contact, the former takes some electric fluid from the latter, which, on its opposite side, it shares with other bodies in the first experiment it shared this fluid with the condenser, while the ground restored it to the copper disc; in the last, zinc communicating that acquisition to the ground, took more fluid from the copper disc, which made the condenser partake of its loss. This is the leading thread with respect to the motion of the electric fluid in the pile, and I shall follow it; but I must first speak more particularly of the anomalies observed in these experiments, which are important.

These differences, sometimes very great, in the quantity of effect of the same operations, surprised me at first; and suspecting something amiss in the condenser, I examined it closely, without finding any defect: then at other times, without any change, I found the same effects. At last I remarked that, commonly, the greatest effects in the same day were in a part of the morning, and the smallest towards the evening; and that these effects differed also in intensity on different days. Now this is what I have said above of the spontaneous effects of the pile, which is composed of a succession of the same binary groups of metals; and thus the condenser, when applied to these experiments, is also a meteorologial instrument. And there is a remarkable circumstance in this respect; that often at the same moment there is a great difference between the effects on the condenser of the opposite extremites of a small pile; but sometimes it is the negative side which prevails, and at other times it is the positive. This manifests, that the ground, with which the opposite side of the small pile communicates, in the former case possesses less, and in the latter more of the electric fluid than the ambient air. But this will be one of the subjects of the following paper.

After having shown distinctly what are the electric effects produced by the conjunction of zinc and copper, and in what manner the condenser manifests these effects, I come to their propagation from each group along the pile, on one side negative and on the other positive. The following experiments will show the first steps, which will be easily extended through the whole.

Exp. 33.-Upon a zinc disc, of the same size as the others, I fixed a piece of Dutch gilt paper, the copper side next to the zinc, and the paper outside, held by a little paste all around. This association is to represent one group of the pile, considered for the present only on the copper side with the paper, which, in the pile, separates it from the next group on this side, and more directly from the zinc plate of that group. Holding on my hand the zinc side of the former group, I repeated. on its paper with the insulated zinc disc, the alternate contacts with the condenser; and by twenty repetitions a sensible negative divergence was produced in the electroscope of the latter. The same effect takes place in the pile at the copper side of every group; it takes, through the paper, some electric fluid from the zinc of the next group; but as zinc must always possess more of this fluid than the copper with which it is con

nected, the zinc of that next group takes more from its own associated copper, which then through the paper, takes more from the zinc of the following group; which effect goes on increasing, up to the end of the pile on this side. I shall only add to this experiment, that, as the property of a group composed of zinc, copper, and paper on the latter, is to have this side negative, whatever be the metal with which the above alternate contacts are performed, they produce the same negative effect on the condenser.

In order to complete directly the first step here in view, by taking one group as an example, it would be desirable, that by placing a piece of paper on the zinc side of this group, in order to represent the separations of the groups in the pile in that direction, it should manifest directly by the condenser, that zinc yelds some electric fluid to the next group; but I have not been able to obtain such a direct proof, on account of a circumstance which I shall now indicate, as peculiar to that quantity of electric fluid set in motion by the property of the pile. This motion is very slow compared with the motion of an external quantity of electric fluid. The smallest degree of electrification of an insulated body, positive or negative, such as can only affect the gold leaf electroscope, communicated to one side of a pile, is instantly manifested at the other extremity; but it is by no means the same with respect to the electric fluid set in motion by the property of the pile: when the electroscopes diverge equally at the extremities, having touched one of them, which makes the gold leaves fall here, and rise more on the opposite side, it requires a time, often very long, before the same divergence is restored. This is the reason why I was obliged to fix twenty seconds for the duration of the contacts of my piles of twenty groups with the condenser, in order to be certain that the maximum of effect was produced; it requires more or less time, according either to their nature, or to the extremity applied to the condenser; but I found, that the slowest was produced in twenty seconds, which made me fix that time.

This will explain the case abovementioned, that there is no sensible effect on the condenser by any number of alternate contacts of an insulated body, with the paper laid on the zinc side of one group; and even when the groups are multiplied to increase the effect, it requires, to make it sensible, a prolongation of the contact on the little pile, in order to give time for the effect to be propagated; as will be seen by the following experiment.

Exp. 34. Made with a portion of my pile of ten groups of 1.6 inch diameter, successively tried by each of their extremities, the opposite one being placed on the movable pillar of my condenser, and the alternate contacts being made with a small insulated disc of the same diameter.

1. No number of alternate contacts, between either of the extremities of the little pile and the condenser, produced any sensible effect on the latter when rapidly made, or in the manner they are executed between the two naked discs, zinc and copper.

2. On repeating the experiment, with the zinc side on the pillar,