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is now minus, of the same quantity (sensibly) as it was at B in the case of Table I, and the quantity minus is doubled at B; a state represented by Table III. I do not know any theory on invisible causes, which more exactly follows the visible effects.

What remains to be considered is the physical cause of these phenomena, all originating in this circumstance, that when zinc and copper are in mutual contact, zinc possesses more electric fluid, and copper less, than in another situation. In

my
first
paper

delivered to the Royal Society, I explained this effect by analogy with the phenomenon of the different capacities of bodies for the fluid cause of heat; but having here entered into an explanation of the nature of the electric fluid, I shall derive analogies from the subject itself.

Most of the electric phenomena manifested in our experiments depend on the distinction which I have established between the density of the electric fluid, consisting in the proportional quantity of electric matter and its expansive power, depending on the quantity of vector. This distinction is particularly manifested by the changes that happen along an insulated conductor of some length, when an electrified body is placed at some distance from one of its extremities. It is known in general, that the extremity of such a conductor next to an electrified body acquires an electric state contrary to that of the body, while its opposite extremity has the same electric state as that body: for instance, suppose the electrified body to be positive, it is commonly said, that the extremity of the conductor next to this body becomes negative, and the opposite extremity positive ; but these are vague expressions, and as they give no real idea of the effects, they have occasioned the variety of systems, all unsatisfactory and therefore changing, hitherto made on these phenomena.

The cause of obscurity on this object is the want of that distinction above mentioned, between the expansive power and the density of the electric fuids belonging to its nature, as expansible. Every fluid of this class, when confined within a certain space,

has necessarily the same degree of expansive power in every part of this space, since this is attached to the very idea of expansibility ; but it is not the same with respect to density. For instance : a mass of air, confined in a certain space, has certainly, in all its parts the same degree of expansive power, whatever change may happen in its partial density. If then a hot body be placed near one side of this mass of air, its density will diminish in this part, and increase in the more remote: or if a piece of ice be brought on one side of this mass of air, its density will increase near the ice, and diminish in the remote parts ; but the degree of expansive power of this confined air will always be equal in all its parts at the same time, increasing or diminishing in the whole.

The case is exactly the same with respect to the electric fluid on an insulated conductor : an insulated positive body being placed

near one part of the latter, this part receives some of the vector which forms around the positive body a kind of atmosphere, as the hot body has around it an atmosphere of igneous fluid : and the former produces an increase of the expansive power of the electric Auid on this part of the conductor, as the hot body produces it in the air next to it. A negative body produces also an effect analogous to a piece of ice : for as this absorbs a part of the free fire in the parts of the mass of air next to, so the negative body absorbs a part of the vector from the electric fluid on the nearest part of conductor. Now, all these changes in the degree of expansive power in both

fluids are attended with inverse changes in their density.

Nobody will doubt of the above statement who has repeated the experiments described in my works; and I may say, that every one of the great number of persons, in whose presence I have made these experiments, with the set of small electric instruments described in my Traité élémentaire sur le Fluide Electro-galvanique, has been convinced of this important distinction between the density and expansive power of the electric fluid. It is not therefore for want of progress in the science itself, that such a variety of systems subsists concerning the electric phenomena; it is for want of attention in most experimental philosophers, by whom, though writing on electricity, my published experiments are never mentioned, not so much as to criticise them, or their conclusions. Among the variety of these experiments, I have here chosen those concerning the modifications which take place on a long insulated conductor; and I come now to the particulars, which will prove all that I have stated above.

Three electroscopes are used in that series of experiments, one of which, a movable one, consists of silver laminæ, suspended on small axes, in order to prevent their motion out of the line of their divergence. Of the two other electroscopes, consisting of small pith balls suspended by silver wires, one is permanently connected with the extremity of the conductor furthest from the electrified body; the other, held up at the top of a high insulating pillar, is kept, by means of a thin wire, in constant communication with the movable electroscope : the latter, though principally destined to move along the conductor, may be removed, from every point, to a distance, in order to try the nature of the divergence that it had at this point, which it does not lose on removal. Lastly an insulated brass disc is the electrified body. The following are the phenomena observed, in which must be recollected what I undertake to prove, namely, that the divergences of the electroscopes are produced by plus or minus of electric matter only, comparatively with the standard, which is the actual proportionate quantity of electric matter possessed by the ambient air; an object connected with the proof of the fundamental proposition, that there is an absolute distinction between the density, and the expansive power of the electric fluid.

1. At the beginning of the experiment, the movable electroscope

is placed near that extremity of the conductor, to which the disc, after having received a spark from a Leyden vial, is to be approximated. At the approach of this positive body within a small distance, the silver laminæ of this electroscope diverge as negative ; some of their electric matter having receded to the remote parts of the system (by this word I express the conductor and its associated electroscopes ); and thus, though the expansive power of the electric fluid has equally increased upon its whole extent, the two remote electroscopes, and in particular that which is connected with the silver lamine, diverge positively by a certain quantity.

2. When the silver laminæ are made to recede from the positive body along the conductor, their negative divergence gradually diminishes ; it ceases at a certain distance, and farther than this begins a positive divergence, which increases to a certain maximum ; nevertheless the remote electroscopes, and in particular that which is in immediate connection with the laminæ, remain positive to the same degree as at first. The effect, therefore, of withdrawing the lamina has been to remove them out of the atmosphere of vector of the positive body, which, by increasing the expansive power of their electric fluid, had made a part of their electric matter to abandon them: and it is the electric matter retired from the anterior part of the system which occasions the positive divergence in the remote electroscopes.

3. While the movable electroscope is thus removed from the atmosphere of the positive body, if any part of the system be touched with a small wire held in the hand, the expansive power of its electric fluid is thus placed in equilibrium with that of the ground, and the divergence ceases in all the electroscopes. Which shows, that, in the parts of the system over which the atmosphere of the positive body does not extend, the equilibrium of proportional quantity of electric matter has been also produced. If then the silver laminæ be moved toward the positive body, when they arrive within that atmosphere they begin to diverge as negative ; and this divergence continuing to increase, it is greater when this electroscope arrives at the end of the conductor, than it had been in the same place at the beginning of the experiment. However, the remote electroscope in communication with this remains without divergence; because the small quantity of electric matter newly withdrawn from the silver laminæ is insensible upon the whole system.

4. Now will come a proof (among many others which may be found in my works), that the divergence in the electroscopes depends only on the proportional quantity of electric matter, or density of the fluid. If, in this state of the system, the silver laminæ be touched with a wire held in the hand, though this contact places them in communication with the ground, their divergence continues the same : because their electric fluid, by the increase of vector proceeding from the positive body, being in equilibrium of expansive power with that of the ground, no electric matter can ascend to them

from the latter, and they remain deprived of it to the same degree.

5. Lastly. If the positive body be removed or discharged, the three electroscopes diverge as negative. By the contact of the system, during the influence of the positive body, which had increased the expansive power of the electric fluid over the whole, the quantity of electric matter which had retired from its anterior parts had passed into the ground; and now, when the influence of the positive body has ceased, this deficiency of electric matter becomes common to the whole system.

Having now, by this series of experiments, demonstrated the fundamental proposition, that an equilibrium of expansive power of the electric fluid may subsist, between two insulated bodies in mutual contact, with a difference in its density, or proportional quantity of electric matter, I come to my system of the electric states of zinc and copper, when, being insulated, they are in mutual contact, which system is founded on that proposition.

It is evident, that the electric fluid must be in equilibrium of expansive power on this group composed of zinc and copper; therefore, the difference observed in their electric states must proceed from a difference in the density of the fluid. Now the only hypothesis added in my system to this immediate conclusion from fact is this : that, during their connexion copper has the property of acquiring more vector than zinc, from that diffused in the ambient air; by which proportional increase of expansive power, the electric fluid on copper is in equilibrium with that on zinc, though with less density, or proportional quantity of electric matter. I have shown also in the above mentioned works, by deduction from experiment, that, when this influence of bodies on each other, by plus or minus of vector, has ceased by sufficient distance, each of them possess instantly, by the effect of the ambient medium, a quantity of vector, proportional to its quantity of electric matter; and thus it is, that the modifications produced by zinc and copper on each other while associated, and their effects on bodies brought into contact with them on the outside of their groups during their association, are converted into modifications of the quantity of the electric fluid itself.

After having treated here the theoretical part of the subject more fully than I had done (for brevity's sake) in my first paper given to the Royal Society, in order to be better understood on this subject, very important in natural philosophy, I return to the experiments concerning the analysis of the galvanic pile, to bring them here to the same point as they were at in that paper.

Having found, by the experiment related at the end of the first part of this analysis, that by increasing the size of the plates, the divergence did not increase in the electroscopes, I considered the manner in which a great number of small plates might be used. I thought then of having a hole in the centre of small plates, in order to thread them with silk in form of chaplets, alternating the plates

with equal pieces of Dutch gilt paper. Not yet having any but tinned iron plates for these trials, I formed two such chaplets, each composed of 140 groups, of 0.5 inch diameter, and in order to guard them against dust, I enclosed them in glass tubes : but I found, that, when the chaplets lay along the glass, the effect was diminished, and in order to prevent this defect, I took larger tubes, with metallic caps, through which, by screws, I kept the chaplet fixed in the axis of the tube; these screws, being on the outside in the form of hooks, served to link the chaplets together. Each of these small instruments acted immediately on the gold leaf electroscope, and, by hooking them together, the effect was doubled.

I founded at that time, on this experiment, the plan of increasing the power of the new instrument so as to produce the divergence of small metallic balls, especially by using zinc plates, which I knew then could be procured. For this purpose I thought of lessening the expense occasioned by the metallic caps for the glass tubes, by making much longer chaplets, and of suspending these in the form of garlands, to the ceiling of the room, by silk strings, bringing only wires from their opposite extremities to a proper place, where the apparatus of the small metallic balls should stand.

Such is the point at which I had arrived the 30th of May, 1808 ; and this object was much forwarded in my paper under the title of The Electric Column and Aerial Electroscope, delivered to the Royal Society the 7th of March, 1809; but the Committee of Papers not having ordered it to be published in the Phil. Trans., it will now appear in a more advanced state. The consequence of its not appearing at the time it should have done is, that my electric column has lost the merit of novelty ; for, by the communications of the minutes at the meetings of the society and the committee, it had attracted attention; and the sight of it, which I did not refuse, has made it sufficiently known to be already imitated. However, while its connexion with the analysis of the galvanic pile is not considered, its principle object is lost : and moreover, till the sticking of the small metallic pendula, when striking, was prevented, which I have obtained but lately, it could not be ranked among meteorological instruments. These particulars will be seen in my following paper.

(To be continued.)

Researches on the action of the Alkaline Peroxides on the Metallic

Oxides. Letter from M. Ed. FREMY to M. PELouze.* The evident analogy which exists between iron and manganese would lead to the supposition that we may one day produce with iron all the compounds which have been obtained with manganese.

It is for this reason that I have thought that it would be possible to form salts in which an oxygenated compound of iron would play

Compte Rendu.

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