TRANSACTIONS OF SECTION A. 447 



, 2-404* 



47r/x CR' 

 If r be the time iu -n-hicli the amplitude sinks in ratio e : 1 



_ 1 47r/x Ci?- 

 '" n " (2-404)2 



For copper iu C-G./S. measure C= , /i = l, 



J?" 

 and thus t = ■ — - nearly 



800 ^ 



In order that t should he one second, the diameter of the cylinder would have 

 to be about two feet. 



3. On the Equilibrium of Liquid- conducting Surfaces charged with 

 Electricitij } By Professor Loed Ratleigh, F.E.S. 



4t. On a Neiv Hand Dynamo-Machiiie. Bij W. H. Preece, F.B.S. 



The author described a compact dynamo-machine designed by the Baron de 

 Meritens for lecturing, teaching, and laboratory pin-poses. It consists of a Pacinotti 

 armature rotating in an electro-magnetic iield of the Gramme type. It gives a 

 continuous current and produces an electromotive force of 70 volts. The resis- 

 tances of the armature and of the field magnets are 4 ohms each. One man can 

 thus produce a current of one ampere through an Edison incandescent lamp with 

 great ease, and four men can illumine four such lamps. The cost of the instrument 

 was 350 francs in Paris. 



5. 0)1 Secondare/ Batteries, ivith special reference to Local Action. 

 By J. H. Gladstone, Ph.D., F.R.8. 



The elements of which a Plants battery and its various modifications consist 

 are metallic lead, peroxide of lead, and dilute sulphuric acid. The reaction that 

 takes place is the combination of the positive metal with SO^, forming PbSO^, 

 and the reduction of the PbO„ by means of the hydrogen to PbO, which in the 

 presence of sulphirric acid is also converted into sulphate of lead and water. The 

 amount of force which can be obtained from a cell depends upon the amount of 

 peroxide of lead which is capable of being reduced. Now the negative plate of 

 these secondary batteries is itself an arrangement of lead and lead peroxide, and if 

 immersed in dilute sulphuric acid galvanic action is at once set up. This ' local 

 action ' is, fortunately, soon diminished by the formation of the badly-conducting 

 sulphate of lead upon the surfaces of the lead plate and crystals of peroxide. 

 When the two plates are brought into connection the discharge takes place be- 

 tween them, but the local action on the negative plate is not stopped. This is 

 shown by the much larger amount of sulphate of lead produced on the negative 

 than on the positive plate. In three experiments in wliich the resistance was 

 varied this increase amounted to 15, 34, and 53 per cent, respectively. The 

 amount of available peroxide of lead that may have been thus destroyed on any nega- 

 tive plate is not easily recognised, for the electromotive force is not affected, and the 

 current obtainable in the first instance is not much reduced, though of course the 

 same amount of work cannot be got out of the battery. 



This local action takes place also during the formation of a cell. One of the 

 proofs of this is that much more oxygen is absorbed than could possibly be 

 absorbed in the oxidation of the minium used in a Faure cell ; indeed, in one 

 experiment which was continued for 115 hours, it was found that a small amount 

 of oxygen was being continuously absorbed, though the main action was complete 

 in less than 40 hours. This was attributed to the formation of sulphate at the 

 expense of the lead plate, and its subsequent oxidation. 



As this local action impairs the value of these secondary batteries, it becomes 

 Phil. Mag., September, 1882. 



