ALLESSANDRO VOLTA 



167 



points of contact cancel one another as soon as the circuit is 

 closed. But if a conductor of the second class is included, a 

 steady current is obtained. Volta tested these liquid con- 

 ductors by soaking porous wood or paper in them, thus 

 obtaining them in the form of flat plates. He found that 

 these conductors on touching suitable metals like zinc, give 

 particularly high tensions, but with other metals, such as cop- 

 per, only very low ones, so that they do not fit into the voltaic 

 series, and he recognises that this makes it possible, not only 

 to obtain a continual flow of electricity, which had already 

 been assumed in the experiments with frogs and with the 

 tongue, but also by multiplying the points of contact, to 

 multiply the tensions. 



With this the voltaic pile was invented. Volta made his 

 first announcement on the 20th March, 1800, in a letter to 

 the president of the Royal Society in London, which was 

 afterwards printed in the transactions of this Society.^ He 

 there says: 



*Yes, the apparatus of which I am telling you, and which 

 will doubtless astonish you, is nothing but a collection of 

 good conductors of different kinds, arranged in a certain 

 manner. 30, 40, 60 pieces, or more, of copper, or better of 

 silver, each laid upon a piece of tin, or, what is much better, 

 zinc, and an equal number of layers of water, or of some other 

 humour which is a better conductor than plain water, such 

 as salt water, lye, &c; or pieces of cardboard, leather, &c. 

 well soaked with these humours; such layers interposed 

 between each couple or combination of different metals, such 

 an alternative succession, and always in the same order, of 

 these three kinds of conductors, that is all that constitutes my 

 new instrument; which imitates, as I have said, the effects of 

 Leyden jars, or of electric batteries, giving the same shocks 

 as they do; which, in truth, remains much below the ac- 

 tivity of the said batteries charged to a high degree, as regards 

 ^Phil. Trans., 1800, p. 403. The original letter is in French. 



