462 



Mr, Warren De La Bue 



[Jan, 21, 



up more than six years ago, and is still in action, loss of the fluid by- 

 evaporation having been from time to time made up. But as soon as 

 connection is established, then the chloride of silver parts with its 

 chlorine and the zinc dissolves, and metallic silver is separated, in a 



Fig. 1. 



spongy state, from the chloride, and remains attached to the silver wire, 

 retaining still the form of a rod. Such an element has the electro- 

 motive force of a volt,* nearly (1-03 volt). 



A Volt is that electromotive force which, working through a 

 resistance of one Ohm, would deposit 0*0011363 gramme of silver 

 from a salt of silver; or decompose 0*0000947 gramme (0*00146 

 grain) of water in one second. 



A column of mercury at 0*^ Cent., one square millimetre in section 

 and 1 • 05 metre high, offers a resistance of 1 ohm ; a pure copper 

 wire y^^ inch diameter and 129 yards long offers a resistance of an 

 ohm. 



These cells are grouped together in trays containing twenty or 

 more, and the trays are placed in cabinets containing in some 

 instances 1200 cells, in others 2160 cells ; a cabinet of 1200 cells is 

 shown in Fig. 2. The total number of elements I am about to use is 

 14,400, and these possess a potential of 14,832 volts, which is con- 



* The units adopted for electrical measurements are those of the Centimetre 

 Gramme Second (C. G. S.) ; where the length is 1 centimetre, the mass 1 gramme, 

 and the interval of time 1 second. 



The expression for the volt in this system is 10^ C. G. S. 

 „ „ ohm „ 109 ^^ 



„ „ microfarad „ 10-^^ „ 



For a complete account of these and other units see ' Everett's Units and Physical 

 Constants,' 1879. Macmillan. 



