There is, then, between Mr. Pilleux's experiments and my own so great an analogy that we might draw the deduction therefrom that induced currents in alternating machines have, like those of the Ruhmkorff coil, a definite direction, which would be that of currents having the greatest tension, that is to say, that of direct currents. This hypothesis seems to us the more plausible in that Mr. J. Van Malderem has demonstrated that the attraction of solenoids with the currents, not straight, of magneto-electric machines is almost as great as that of the same solenoids with straight currents; and it is very likely that the difference which may then exist should be so much the less in proportion as the induced currents have more tension. We might, then, perhaps explain the different effects of the wear of the carbons serving as rheophores, according as the currents are continuous or alternating, by the different calorific effects produced on these carbons, and by the effects of electric conveyance which are a consequence of the passage of the current through the arc.
We know that with continuous currents the positive carbon possesses a much higher temperature than the negative, and that its wear is about twice greater than that of the latter. But such greater wear of the positive carbon is especially due to the fact that combustion is greater on it than on the negative, and also to the fact that the carbonaceous particles carried along by the current to the positive pole are deposited in part upon the other pole. Supposing that these polarities of the carbons were being constantly alternately reversed, the effects might be symmetrical from all quarters, although the only current traversing the break were of the same direction; for, admitting that the reverse currents could not traverse the break, they would exist none the less for all that, and they might give rise (as has been demonstrated by Mr. Gaugain with regard to the discharges of the induction spark intercepted by the insulating plate of a condenser) to return discharges through the generator, which would then have, in the metallic part of the circuit, the same direction as the direct currents succeeding, although they had momentarily brought about opposite polarities in the electrodes. What might make us suppose such an interpretation of the phenomenon to have its raison d'etre, is that with the induced currents of the Ruhmkorff coil, it is not the positive pole that is the hottest, but rather the negative; from whence we might draw the deduction that it is not so much the direction of the current that determines the calorific effect in the electrodes, as the conditions of such current with respect to the generator. I should not be surprised, then, if, in the arc formed by the alternating currents of magneto-electric machines, there should pass only one current of the same direction, and which would be the one formed by the superposition of direct currents, and if the reverse currents should cause return discharges in the midst of the generating bobbins at the moment the direct currents were generated.--Th. Du Moncel.
VOLCKMAR'S SECONDARY BATTERIES.
The inventive genius of the country is now directed to these important accessories of electric enterprise, and no wonder, for as far as can at present be seen, the secret of electric motion lies in these secondary batteries. Among other contributions of this kind is the following, by Ernest Volckmar, electrician, Paris:
The object of this invention is to render unnecessary the use in secondary batteries of a porous pot which creates useless resistance to the electric current, and to store in an apparatus of comparatively small weight and bulk considerable electric force. To this end two reticulated or perforated plates of lead of similar proportions are prepared, and their interstices are filled with granules or filaments of lead, by preference chemically pure. These plates are then submitted to pressure, and placed together, with strips of nonconducting material interposed between them, in a suitable vessel containing a bath of acidulated water. The plates being connected with wires from an electric generator are brought for a while under the action of the current, to peroxidize and reduce the whole of the finely divided lead exposed to the acidulated water. The secondary battery is then complete. It will be understood that any number of these pairs of plates may be combined to form a secondary battery, their number being determined by the amount of storage required. The perforated plates of lead may be prepared by drilling, casting, or in other convenient manner, but the apertures, of whatever form, should be placed as closely together as possible, and the finely divided lead to be peroxidized is pressed into the cells or cavities so as to fill their interiors only.