VOLTAIC PILE. 



Fig. 9. 



same superposition of the same combinations of zinc, cloth, and 

 copper, was continued until the pile was completed. The highest 

 disc (of copper) was then the positive, and the lowest disc (of zinc) 

 the negative pole, according to the principles already explained. 



It was usual to keep the discs in their places by confining them 

 between rods of glass. 



Such a pile, with conducting wires connected 

 with its poles, is represented in fig. 9. 



42. As the batteries used on telegraphic 

 lines are liable to frequent removal from place 

 to place while charged with the acidulated 

 water, or other exciting liquid, it has been 

 found desirable to contrive means to prevent 

 such liquid from being spilled, or thrown from 

 cell to cell. This has been perfectly accom- 

 plished by the simple expedient of filling the 

 cells with silicious sand, which is kept satu- 

 rated with the exciting liquid so long as the 

 battery is in operation. 



43. It is often necessary, in telegraphic 

 operations, to vary the intensity of the current. 

 This is accomplished, within certain limits, 

 without changing the battery, in the following 

 manner : 



If it be desired to give the full force of 

 the battery to the current, the wires are 

 attached to the terminal plates, so that the 

 entire battery is between them. But if any 

 less intensity is desired, the wires, or one of 

 them, is attached to intermediate plates, so 

 that they shall include between them a part 

 only of the battery. The part included between them is alone 

 active in producing the current, all the elements which are outside 

 the wires being passive. The battery, in effect, is converted into 

 one of fewer elements. 



Provisions are made, which will be explained hereafter, by 

 which the operator can, by a touch of the hand, thus vary the 

 force of the battery. 



44. The batteries generally used for the English telegraphs 

 are those described in (36). They are usually charged with 

 sand, wetted with water mixed with sulphuric acid, in the pro- 

 portion of about one part of strong acid to fifteen of water. A 

 more intense current could be produced by using a stronger 

 solution, but it is found preferable to augment its intensity by 

 increasing the number of plates in the battery. The dimensions 



133 



