27 



On the Electricity excited by the mere Contact of conducting Sub- 

 stances of different Kinds. In a Letter from Mr. Alexander Volta, 

 F.R.S. Professor of Natural Philosophy in the University of Pavia, 

 to the Rt. Hon. Sir Joseph Banks, Bart. K.B. P.R.S. Read 

 June 26, 1800. [Phil. Trans. 1800, p. 403.] 



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 appa- 

 ratus, 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 con- 

 ducting 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 horizon- 

 tally, 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 re- 

 peated 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 

 pan* 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 elegtrometer, 

 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 suc- 

 cession of small shocks, resembling those occasioned by a Leyden 

 phial, or a battery weakly charged, or by a torpedo in a weak con- 

 dition. 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 some- 



