CHAP. XL] ELECTRICITY AND MAGNETISM. 



383 



in series, giving (for a short time) currents of extra- 

 ordinary strength. A secondary cell resembles a Leyden 

 jar in that it can 

 be charged and then 

 discharged. Its 

 time rate of leakage 

 is also similar. The 

 residual charges of 

 Leyden jars, though 

 small in quantity 

 and transient in 

 their discharge, yet 

 exactly resemble 

 the polarisation 

 charges of volta- 

 meters. 



416. G-rove's 

 Gas Battery. 

 Sir W. Grove de- 

 vised a cell in which 

 platinum elec- 

 trodes, in contact 

 respectively with 

 hydrogen and oxy- 

 gen gas, replaced 

 the usual zinc and 

 copper plates. 

 Each of these gases 

 is partially occluded 

 by the metal pla- 

 tinum, which, when 

 so treated, behaves 



Fig. 154- 



like a different 



metal. In Fig. 155 



one form of Grove's Gas Battery is shown, the tubes 



O and H containing the + and - electrodes, surrounded 



with oxygen and hydrogen respectively. 



