



1892.] and Measurement of Small Electrostatic Capacities. 9 



insulated wire of a short length of submarine cable core, or of 

 telephone, or telegraph, or electric light cable, sunk under water, 

 except a projecting portion to allow external connexion to be made 

 with the insulated wire. 



The electrometer which I find most convenient is my " multi- 

 cellular voltmeter," rendered practically dead-beat by a disc under 

 oil hung on the lower end of the long stem carrying the electric 

 " needles " (or movable plates). In the multicellular voltmeter used 

 in the experimental illustration before the Royal Society, the index 

 shows its readings on a vertical cylindric surface, which for electric 

 light stations is more convenient than the horizontal scale of the 

 multicellular voltmeters hitherto in use ; but for the measurement of 

 electrostatic capacity the older horizontal scale instrument is as con- 

 venient as the new form. 



FIG. 3. 



To give a convenient primary electrification for the measurement, 

 a voltaic battery, VV (fig. 3), of about 150 or 200 elements, of each 

 of which the liquid is a drop of water held up by capillary attraction 

 between a zinc and copper plate about 1 mm. asunder. An ordinary 

 electric machine, or even a stick of rubbed sealing-wax may, how- 

 ever, be used, but not with the same facility for giving the amount 

 of electrification desired as the voltaic battery. 



One end of the voltaic battery is kept joined metallically to a wire, 



