of the fly continually electrifying a number of atoms as abovementioned, just in front of them, and yet continuing replenished with electricity, each point answers to one of the balls in figs. 5 and 6, and the electrified atoms in front of it, to the other ball in the same fig. While the unelectrified atoms, at a distance in front of the point, attract the electrified atoms between them and the point, tending to draw such electrified atoms in that direction, the unelectrified atoms behind the point attract its electricity, and consequently itself, in the opposite direction.

(76.) The mass of electrified atoms from which each point recedes, being continually replaced by others equally electrified, an acceleration of the receding motion takes place, until the motive force is equalled and balanced by the friction of the air and the pivot of the fly.

(77.) I may be allowed to conclude with a hope that my labours may result in sufficient utility to form an excuse, at least, for the imperfections I feel sensible will be found in their execution.

LEAMINGTON, 29TH JUNE, 1839.

CHARLES GRIFFIN.

NOTE TO PROP. 58.- Coulomb's Law, though it may express the attractions between two balls, must not be depended on as a true expression of the forces exerted by electricity on other matter (inductively or otherwise) at a distance, as his balls allowed of a transference of the fluid from one part of the surface to another, thereby changing the position of the centres of attraction. I had begun to prepare for some experiments to ascertain the true forces of attraction, when I was interrupted by ill health, which has added to my natural inaptitude for delicate manipulations; but should be glad to see the matter taken up by some such ingenious and dexterous manipulator as Mr. Snow Harris. It may not be amiss to state here my intended apparatus, &c., as a suggestion to others, viz. :

First, A perfectly spherical ball, with metallic surface, and insulated by a glass leg, coated with melted wax.

Secondly, A hollow sphere, of rather larger diameter, to inclose the other sphere or ball, their centres coinciding, and consequently their opposed surfaces parallel: this sphere, however, divided into hemispheres for the convenience of removal. A small well rounded

hole in this hollow sphere, rather larger than the glass leg of the inclosed ball, for the admission of that leg without contact. A portion of the hollow sphere to be also so cut out as to be capable of admission, as accurately as possible, without actual contact. The piece so cut out to be suspended from the arm of

Thirdly, A delicate balance. A scale at the opposite end of the balance beam, and the whole exactly poised.

B

Fourthly, Small weights for this scale (query), cut from fine wire in multiple lengths.

It is evident that electricity, on the smaller sphere or ball, would exert equal forces on equal spaces of the larger or hollow sphere, including that part of it cut out and suspended from the arm of the balance.

Let the hollow sphere be, say, half an inch from the electrified one; and the attraction being ascertained for the piece affixed to the balance, let the electrified ball be inclosed in another hollow sphere, which shall be, say, an inch from the electrified one, and have a piece cut out and affixed to the balance, bearing the same proportion to the whole as did the piece cut out of the first hollow sphere. The attraction of the same quantity of electricity as was used for the smaller hollow sphere, having been ascertained for the piece cut out of the larger, the proportion they bear to each other will indicate the relative attractions of the same portion of electricity at different distances. Should the attraction be the same for each piece cut out, then a similar attraction will be equal at all distances, and Coulomb's law will apply to this case. I think a whole hemisphere might be conveniently affixed to the balance, instead of cutting out a smaller piece for that purpose, unless (which I think would be best, and perhaps almost necessary,) the electrified sphere should be at least a foot in diameter, and the two hollow spheres of very different sizes.

In the experiments of Coulomb, and those now suggested also, the attractive influence is exercised by induction, or through the medium of other bodies. What it may be between two bodies without any intermedium (as two atmospheric atoms are by others supposed to be), is another question.

By the arrangements above suggested, might also the inductive attraction of different multiple and other portions of electricity, for solid matter at the same distance be ascertained, and perhaps also the forces called repulsive.

Note on the relative Measures of the powers of a Copper-zinc and a Platinum-zinc Voltaic Series. By Dr. M. H. JACOBI, Mem. Imp. Acad. St. Petersburgh.†

I have the honour of communicating to the Imperial Academy of Science, the result of my experiments on the relative powers of two different kinds of voltaic cellular series; the one composed of copper and zinc, charged with sulphate of copper and sulphuric acid, diluted with six times its volume of water; the other, platinum and zinc, charged (after Grove's method) with concentrated nitric acid and sulphuric acid, similarly diluted to that in the former series. The copper-zinc series had 38, and the platinum-zinc series only 2.5 square inches of surface. For the measure of the power, I availed myself of the Balance of Becquerel. This instrument is • M. Becquerel's Balance is fully described in the "Annals of Electricity," &c., vol. 1. page 398.-EDIT.

+ Poggendorff's Annalen der Physik und Chemie.

valuable for accurate measurements, when the wire cylinders are so contrived that they for a counterpoise, are enabled to make the necessary conditions of equilibrium, which is attained when the wire cylinder can so act as to repel the magnetic bar. For this purpose, one of the cylinders must be fastened below that bar, and the other over it. Through the latter hollow cylinder passes a pin or wire, by means of which the magnetic bar is suspended from the arm of the balance. It is necessary, however, to apply a correction to the indications afforded by this instrumental measurement of the powers of the currents. This correction, the necessity of which has been shewn by other contemporaneous labours, is in the proportion of the squares of the powers of the currents. If, for instance, the absolute power of the current be represented by k', and the power indicated by the measuring instrument by k, we shall have this equation: k=k'—y k22, from which we obtain k'= (1—√1—4 k y)

1

2 y

From a series of observations, I found for my equipoise

y= 0.00004228.*

The following table contains the experiments made with the before-mentioned voltaic series. The first column shews the resistance L, offered by the connecting wire which served as the spiral, a resistance which was ascertained by other experiments. The other two columns contain the true powers of the currents; that is, the measured powers, corrected by the above formula :

If A and A' represent the electromotive powers, and X and X the resistances presented by the series themselves, we shall have, according to the formula of Ohm,† these four equations

Poggendorff's Annalen, Bd. xlvii., s. 225.

We propose to give Professor Ohm's Theory of Electric Currents in an early number.-EDIT.

Or, if we take λ, which, in this case, is 36 square inches, for the unit of surface,

If s represent the whole surface of the pile, z the number of pairs, c the strength of the current, L any resistance,

S

From this equation, we learn that the maximum of power of Z 2λ the current is obtained, when the pile is so managed, that = L; that is, when the whole resistance of the pile is equal to that introduced into the pile itself, in addition to the foreign resistance of the conductors. Hence, for any other arrangement than that which answers to a maximum of action, no constant relation between the different voltaic combinations are extant; nor can we, under any other circumstances, form a correct judgment of their relative superiority. By the elimination of z we have

from which, after substitution of the former for A, A', λ, λ', their values are found to be

For the whole surface s's 0'06,

And in reference to the number of pairs z'z 0·6;

that is, we need only a pile of six square feet of platinum surface, in order to supply the place of a pile of a hundred square feet of copper surface; or, in reference to the number of pairs:-Six pairs of platinum, of a square foot of surface each, give the same action as ten pairs of copper of ten square feet of surface each. This extraordinary superiority of platinum has been well confirmed by other experiments.*

* At the time I received the above note, its author sent me a leaf of the Journal de St. Petersburg, in which he states that the electro-magnetic powers of a Grove's battery would become applicable to navigation. The battery of which he speaks, consists of 64 pairs of platinum plates, each plate 36 square inches of surface; so that the whole platinum surface is 16 square feet. This is probably the mightiest battery that has hitherto been constructed, the great battery of the London Institution, of 2000 pairs of plates, and 1000 square feet of surface, not excepted. Notwithstanding the extraordinary powers of its thermo-chemical and dynamic action, the physiological effects of this great battery, as shown by Schönbein's small one of six pairs of plates, are only feeble. The action on the human body is discernible, but is easy to bear. We must remark, in this place, that the author does not look upon this phenomenon as a specific quality of the platinum battery, nor as an anomaly; since it finds an explanation in Prof. Ohm's mathematical laws of the galvanic battery.-Poggendorff.

On the Observations of M. BECQUEREL, relative to the Comparative Measures of Action of two Voltaic Series; the one Copper-zinc, the other Platinum-zinc. By Dr. M. H. JACOBI, Mem. Imp. Academy St. Petersburg, &c. &c.

At the sitting of January 13th, of last year, I had the honour of presenting a note to the Academy, on the measurement of the comparative action of two distinct voltaic series, the copper-zinc, and the platinum-zinc. This note has given rise to some observations by M. Bequerel, at the Academy of Sciences, Paris, on the 4th January last, in which he thus expresses himself:

"It seems from this conclusion, that in piles in general, platinum is far superior to copper for transmitting large quantities of electricity. But this superiority, in the present case, is due to a condition which M. Jacobi has not noticed, although it exercises a considerable influence on the action of the pile, which is sometimes neglected by experimentalists."

M. Becquerel attributes the superiority of the platinum series to the reaction of the concentrated nitric acid upon the acidulated water, which gives rise to an electric current, of much more considerable energy than that resulting from the solution of sulphate of of copper on the similarly acidulated water in the copper series.

M. Becquerel then adds, "I thought it my duty to make these observations, which in other respects are not new, in order that experimenters may not be led into error respecting the causes of the effects obtained by M. Jacobi."

From this observation, one might suppose that, in my note, there was a very serious omission, since M. Becquerel thought it his duty to fill it up. The calculations from my experimental data were made accordingly with the formula of Ohm; and the result shows, clearly enough, the cause of the effects: but to this formula I have thought proper to introduce the expression of the maximum of effect, because it is this expression (till then not noticed) that places us in circumstances which enable us to make accurate comparisons on the action of different voltaic combinations. It is with pleasure that I embrace this opportunity of declaring myself in favour of the theory of M. Ohm, which, in my opinion, is one of the most extraordinary advances in this department of natural philosophy. It collects into one view an immense assemblage of facts; and explains distinctly the whole of the phenomena which relate to the force of voltaic currents. Indeed, this theory has been confirmed and extended by some of the most distinguished philosophers. The law of Ohm, known in Germany for more than thirteen years, is now beginning to spread itself over England, and will give, I hope, a new direction to the zealous experimentalists of that country. In France, the same law, ten years after its publication, was announced as a new discovery, and has been received as such.