Page:Proceedings of the Royal Society of London Vol 1.djvu/47

Rh

In prosecuting his experiments on the electricity produced by the mere contact of different metals, or of other conducting bodies, the learned Professor was gradually led to the construction of an apparatus, which in its effects seems to bear a great resemblance to the Leyden phial, or rather to an electric battery weakly charged; but has moreover the singular property of acting without intermission, or rather of re-charging itself continually and spontaneously without any sensible diminution or perceptible intervals in its operations. The object of the present paper is to describe this apparatus, with the variety of constructions it admits of, and to relate the principal effects it is capable of producing on our senses.

It consists of a long series of an alternate succession of three conducting substances, either copper, tin and water; or, what is much preferable, silver, zinc, and a solution of any neutral or alkaline salt. The mode of combining these substances consists in placing horizontally, ﬁrst, a plate or disk of silver (half-a-crown, for instance,) next a. plate of zinc of the same dimensions; and, lastly, a similar piece of a spongy matter, such as pasteboard or leather, fully impregnated with the saline solution. This set of three-fold layers is to be repeated thirty or forty times, forming thus what the author calls his columnar machine. It is to be observed, that the metals must always be in the same order, that is, if the silver is the lowermost in the ﬁrst pair of metallic plates, it is to be so in all the successive ones, but that the effects will be the same if this order be inverted in all the pairs. As the ﬂuid, either water or the saline solution, and not the spongy layer impregnated with it, is the substance that contributes to the effect, it follows that as soon as these layers are dry, no effect will be produced.

This apparatus, when it consists of only twenty pairs of metallic plates, is already capable not only of giving to Cavallo's electrometer, with the aid of a condenser, signs of electricity as high as 10° or 15°, and of charging the condenser by a simple touch to such a degree as to give a spark; but it will also give to two ﬁngers of the same hand, the one touching the foot and the other the top of the column, a succession of small shocks, resembling those occasioned by a Leyden phial, or a battery weakly charged, or by a torpedo in a weak condition. These effects will be increased if the communication be made through water; for which purpose the bottom of the column may be made to communicate, by a thick metallic wire, with water contained in a basin or large cup. A person who now puts one hand into this water, and with a piece of metal held in the other hand touches the summit of the column, will experience shocks and a pricking pain as high as the wrist of the hand plunged in the water, and even