Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7. Fig. 8. Fig. 9. Fig. 10. Fig. 11. Fig. 12. Fig. 13. Fig. 14. Fig. 15. Fig. 16.

Engr. by W.B. Lines Edinburgh. Published by A. Constable & Co. 1820. cohol interposed between the poles of this same pile does not discharge it completely; it leaves a tension remaining at its poles, and we can repeat with it the experiments of Mr Hermann. This flame, then, does not conduct the electricity so well as the alkaline soap.

From the details which we have given in this article, it appears that the electromotive apparatus may be considered, as producing by the mutual contact of the heterogeneous bodies which compose it, a developement of electricity, which is propagated and distributed through its interior by means of the conductors interposed between its metallic elements. If we form a communication between its two poles, the discharge which follows, overturning the state of electrical equilibrium in the series of bodies superimposed on each other, causes them to be recharged according to the conditions of this equilibrium, either at the expense of the ground, or by the decomposition of their natural electricities. The repetition then of such discharges, or rather their continuation, must occasion in the apparatus a continued electrical current, the energy and the quantity of which depend as well on the magnitude and the nature of the metallic elements in contact with each other, as on the greater or less facility which the conducting parts of the apparatus present to the transmission of electricity. Setting out from these primary notions, we have described the most favourable arrangements for obtaining from the Voltaic apparatus each of the electrical, physiological, and chemical effects which it is capable of producing; and we have confirmed our views of the subject by relating those experiments, which prove them to be conformable with the actual fact. The general result of these researches has shown, that the action of this apparatus depends on two elements, of which the one, constant in its energy, consists in the electromotive faculty of pieces of metal, and the other, which is variable, depends on the more or less perfect conductivity of the bodies interposed. The first of these elements has been fixed by Volta, by help of experiment, and in a manner which seems to us to leave not the smallest doubt of the fact. But the second, in the variety almost infinite which belongs to it, presents to the researches of philosophers a field for an infinity of experiments, the results of which, enabling them perhaps to augment still farther the power of this instrument, may furnish extremely curious data as to the conditions which determine the easy or difficult passage of electricity through bodies; as to the manner, hitherto unknown, by which it attaches itself to their particles; and, perhaps also as to the nature of electricity itself, or at least the condition in which the principle that produces it exists in bodies.

Since this article was written, a young French philosopher, Mr Becquerel, has made a series of extremely curious experiments, in regard to the production of electricity by compression. He forms very slender discs of any substances,—insulates each of these discs at the extremity of a tube of glass, or of resin well dried, and taking one of these tubes in each hand, presses against each other two of the discs, of a different nature, and withdraws them from their contact in opposite states of electricity; the one becomes vitreous and the other resinous. This phenomenon must not be confounded with the developement of electricity by simple contact, such as Volta made use of in his excellent researches. It is incomparably more powerful with almost all substances: A single pressure is sufficient, in ordinary cases, to drive off with rapidity the moveable disc of the electroscope of Coulomb (see Electricity, Supplement); and the repetition of several pressures is sufficient to charge powerfully and directly, an ordinary electroscope with gold leaves, without the aid of the condenser. Cork, bark, hairs, paper, and wood, produce these phenomena with a very high degree of intensity. The same takes place equally well with most of the minerals. Some bodies appear to have the property of reacting on themselves, when electrified in this manner. They decompose their own electricities; and these, once developed, fix, by their influence, that which is disengaged at their surface. In a word, these bodies act, in reality, unto themselves like condensers; so that we may take them in the hand, or even moisten their surface without depriving them of their electricity. No substance possesses this faculty in a higher degree than the rhomboidal carbonate of lime; and, indeed, Mr Hauy has long since found, that it is sufficient to press slightly between the fingers a crystal of this mineral, to cause it assume a very powerful state of electricity, which it then preserves with obstinacy for hours, and even for whole days, without requiring any renewal. Mr Becquerel has also found that many minerals may be electrified by mere exfoliation. A thin leaf of mica, for instance, if separated into two others, held by two insulating tubes, these two are found to possess, in a high degree, the opposite states of electricity; the one is resinous, the other vitreous; and many substances which are incapable of producing this opposition, when exfoliated at the common temperature, acquire this property when they have been moderately heated. (z. z.)