448 Mr. G. W. Wigner on Grove's Battery. 



trying. The luminous phenomenon was frequently so brilliant 

 as to make it appear as if there was an actual luminous arc ; but 

 when the circuit was opened and the conduction examined in the 

 usual manner, it was found to be a mere ignition with contact 

 between the poles. 



If D were quite constant and independent of the intensity, the 

 least electromotive force by which a luminous arc could have 

 been produced must have been greater than D, as determined 

 by the stronger currents. This is obvious ; and it follows, more- 

 over, that if with a given value of E a luminous arc can be 

 produced, this is no longer possible if the resistance is adequately 

 increased. Hence a certain intensity is necessary to produce a 

 luminous arc. Comparing the values of D as determined by 

 stronger currents with the limiting values of E by which a lumi- 

 nous arc can just be produced, it is observed that with the hard 

 carbon-points in Series 1 the electromotive force E of the battery 

 is greater than D, but in all the other series E is either just as 

 great as, or is smaller than D. If the values of D in all the five 

 series are added, and in the same way the limiting values of E, 

 the sum in the first case is 20*57, and in the other 19*57. Hence, 

 as the result of this investigation, we may establish the principle 

 that D, which is constant with powerful currents, diminishes with 

 smaller ones* 



LIII. On Grove's Battery. 

 By G. W. Wigner, F.R.A.S* 



N the course of a large number of experiments with Grove's 

 batteries in which great electromotive force was required, 

 several modifications of the usual arrangement have suggested 

 themselves to me, which have had the effect of greatly increasing 

 the power of the battery, increasing the constancy of the current, 

 and diminishing the labour of charging the cells. 



The first object sought was to diminish the internal resistance 

 of the battery ; and this was attained in four ways. 



(1) The upper face of each zinc plate (to which the pla- 

 tinum plate is screwed) was carefully filed oft" to a perfectly 

 smooth and flat surface, and the screws were tightened as much 

 as possible. A large contact-surface was thus secured instead 

 of the few points at which it is usually obtained. The oxidation 

 between the two plates was also greatly diminished by this. The 

 contacts of course were carefully cleaned every time the battery 

 was used. 



(2) The thickness of the platinum plates was increased, as it 



* Communicated by the Author. 



