ELECTRICITY. 388 



This effect is greatly increased by employing 

 many alternations of substances proper for the pur- 

 pose. Thus if in a glass tube there are regularly 

 arranged alternating plates of silver, zinc, and thin 

 paper, having one end terminating with a zinc 

 plate, and the other with a silver plate, and the 

 opposite ends of the tube be laid upon electro- 

 meters ; it will be perceived that one electrometer 

 will be affected by negative, and the other by po- 

 sitive electricity. 



Plate 26. fig. 6. represents this arrangement. 



But if a solution of salt, or a diluted acid be 

 employed as one of the alternating substances, the 

 indications of electricity will be much more evi- 

 dent. It was in this way that Volta constructed 

 that which has since been denominated the Voltaic 

 pile or battery. 



Take a number of plates of copper, or, what is 

 better, of silver; and an equal number of tin plates, 

 or, what is still better, of zinc ; and the same 

 number of pieces of card, leather, or woollen cloth, 

 the last of which seems to answer the best. Let 

 these last be well soaked in common water, or 

 rather, in a solution of common salt, sal ammoniac, 

 nitre, or nitrous acid. The silver or copper may 

 be pieces of money, and the zinc pieces may be cast 

 of the same size. A pile is to be formed of these 

 substances in the following manner: a piece of zinc, 

 a piece of silver, and a piece of wet cloth, or card ; 

 then another piece of zinc, a piece of silver, and a 

 piece of wet cloth ; and so on in the same order, 

 till the number required has been placed. But, as 

 the pieces, when unsupported, are apt to fall down 

 when their number is considerable, it is best to 

 support them by means of three rods of glass, stuck 

 into a piece of wood, and touching the metallic 



