58 



Mr. J. Parnell on Secondary Currents 



14. The interposition of flannel between the plates of the ex- 

 perimental copper-" soda " couple having shown no tendency 

 to diminish its force*, a forty-cell secondary battery was con- 

 structed, each couple of which consisted of two plates of copper 

 separated by flannel, each plate presenting an effective surface 

 of 516 square centims., and was immersed in a solution of 

 " soda," spec. grav. 1050. This battery was arranged in ten 

 sets of four cells each, and each set was connected in series. A 

 commutator was devised for the purpose of charging this bat- 

 tery as ten compound cells, and discharging it as forty cells in 

 series. This instrument, shown in plan in fig. 2, consists of a 



Fig. 2. 



A„ 



— T 



A-io 



-Rxo 



A 9 



-R 9 



A 8 



-». 



A 7 



~ Rt 



A 6 



-■*. 



A 5 



- * 5 



A 4 



- R< 



A 3 



-B. 



A 2 



- R 2 



A T 



- R t 



horizontal cylinder of ebonite, H H, attached to two vertical brass 

 supports, P and N, and capable of being made to rotate about 

 its axis through an angle of 90°. The supports P and N are 

 fixed to an ebonite stand, G K, and are provided with screws for 



* Although I could not, after repeated excitations during many months, 

 observe any deterioration in the condition of the flannel, yet no doubt an 

 electrolytic action had taken place, as a purple dyeing-substance was pro- 

 duced, which gave a deep violet tint to the flannel and solution, the latter 

 becoming fluorescent. We shall see further on that when a powerful ex- 

 citing battery is employed, flannel is not suited to the purpose required. 



