384 GALVANISM. 



pieces at three equally distant points, as repre- 

 sented in Plate 21. fig. 7. Down these rods may 

 slide a small circular piece of wood, having three 

 holes in it, and which will serve to keep the top of 

 the pile tight, and the different pieces in close con- 

 tact. The moistened pieces should likewise be 

 somewhat less than the pieces of metal, and though 

 they should be well moistened, they should be 

 gently squeezed before they are applied, that the 

 superfluous moisture may not run down the pile, 

 or insinuate itself between the pieces of metal. 



The instrument, constructed in this manner, 

 will afford a constant current of the electric fluid, 

 through any conductor communicating between 

 the uppermost and lowest plate ; and, if one hand 

 be applied to the lowest plate, and the other to the 

 upper, a shock is felt, which is repeated as often as 

 the contact is renewed. An objection to this con- 

 struction of the pile, or battery, is the trouble of 

 placing the pieces in the proper order, and also 

 that of cleaning the pieces of zinc, which are 

 rapidly oxydated. The best method of doing this 

 is by a file, or by putting them into diluted muri- 

 atic acid, which dissolves the oxyd. 



The battery, Fig. 8., consists of a row of wine- 

 glasses, or cups, containing salt and water, or sul- 

 phuric acid and water. Into each of these is 

 plunged a plate of zinc, and another of silver or 

 copper. These plates are made to communicate 

 with each other by means of a thin wire, fastened 

 so that the silver of the first glass is connected 

 with the zinc of the second, the silver of the 

 second with the zinc of the third, and so on pro- 

 gressively through the whole chain of glasses. 

 When one hand is dipped into the first glass, and 

 another in the last, the shock is perceived. 



