380 Intelligence and Miscellaneous Articles. 



of sufficient dissemruation. — Bull, de VAcad. Eoy. de Belgique, 

 ser. 3, tome ii. no. 7 (1881). 



ON SECONDARY BATTERIES. BY J. ROUSSE. 

 In order to accumulate electricity so as to produce electric light 

 or motive force, I have arranged several secondary batteries which 

 differ notably from that of M. Gr. Plante. 



(1) At the negative pole of the secondary battery I employ a 

 palladium plate, which, during the electrolysis, absorbs more than 

 900 times its volume of hydrogen. At the positive pole I employ a 

 plate of lead. The liquid electrolyzed is sulphuric acid diluted to 

 10 per cent. This element is very powerful, even when of small 

 dimensions. 



(2) Another secondary element, which has also given good 

 results, is formed, at the negative pole, of a thin plate of sheet- 

 iron : this absorbs more than 200 times its volume of hydrogen 

 when it is electrolyzed in a solution of ammonium sulphate. The 

 positive pole cousists of a plate of pure lead coated with litharge, 

 or with pure oxide, or white-lead, or with a mixture of all these sub- 

 stances. These metallic plates dip into a 50-per-cent. solution of sul- 

 phate of ammonia. 



I have also employed, with some success, other similar combina- 

 tions. Eor example : — 



At the negative pole a plate of sheet-iron ; at the positive pole 

 a cylinder of ferromanganese. The liquid electrolyzed is sulphate 

 of ammonia at 40 per cent. 



I have remarked that, in general, for composing a secondary bat- 

 tery it is sufficient to place at the negative pole of the voltameter a 

 metal which possesses the property of absorbing hydrogen when it 

 is placed in a suitable solution. On the other hand, it is necessary 

 to place at the positive pole a metal which absorbs oxygen and 

 becomes peroxidized. — Comptes Renclus, Oct. 3, 1881,t.xciii.p.545. 



ELECTRICAL TESTING. 

 To the Editors of the Philosophical Magazine and Journal. 



Electrician's Department, General 

 Gentlemen, Post Office, Oct. 4, 1881. - 



In your issue for October last (no. 75, vol. xii.) I notice an article 

 by Mr. Thomas Gray, " On the best Arrangement of the Wheat- 

 stone's Bridge for the Measurement of a particular Resistance," in 

 which he says, " so far as I am aware, no one has considered in 

 detail all the different cases." I would beg to point out that, in 

 the second edition of my 'Handbook of Electrical Testing'*, pub- 

 lished in the month of June of the present year, I have fully worked 

 out the whole question (including the particular cases referred to 

 by Mr. Gray), and I have done this without the use of the calculus ; 

 moreover I draw attention to the fact that, although the calculus 

 method shows the conditions for obtaining an absolute maximum 

 of sensitiveness, yet it does not show (as I have done) that this 

 absolute condition may be very widely departed from without tac- 

 tically affecting the sensitiveness of the arrangement. 



Yours faithfully, H. E. Ejjmpb. 

 * Published by Messrs. E. and F. N. Spon, Charing Cross. 



