374 PHYSICS. 



of forming tUe lead oxide upon tlie surface of the lead plates themselves, 

 as Plante has done, the two plates are covered with a layer of red lead 

 held in place by a wrapping of felt. Eeynier liad said that one of these 

 cells weighing 75 kilograms could store up sufficient energy to yield a 

 horse-power of work for an hour. Thomson found the box of electricity 

 brought to him at Glasgow from Paris by Major Seaver, occupying 72 

 hours in the trip, to contain in the space of one cubic foot a million foot- 

 pounds of energy, thus confirming Reynier's statement. Accumulators 

 weighing three-quarters of a ton will work for six hours from one charge, 

 doing work all this time at the rate of one horse-power, with an econ- 

 omy of 90 per cent. {Nature, May-September, 1881, xxiv, G8, 105, 137, 

 156, 433, 491.) 



Sutton has described a new electrical storage-battery, in which he uses 

 a sheet of lead amalgamated and a sheet of thin copper a little shorter. 

 The two sheets are perforated with a number of holes, and then rolled 

 in a spiral separated by rubber bands. The plates are immersed in a 

 solution of copper sulphate, the lead plate being made the positive elec- 

 trode of a suitable source of electricity. The oxygen set free on the 

 lead plate produces peroxide there, the hydrogen reduces the sulphate 

 and deposits copper on the copper plate, the liquid becoming colorless. 

 During the discharge of the battery these actions are reversed. A cell 4 

 inches deep and 4 inches in diameter heated one inch of No. 28 iron wire 

 to bright redness for over two hours. {Nature, December, 1881,xxv, 198.) 



Sir William Thomson read a paper at the York meeting of the Brit- 

 ish Association upon the proper iiroportions of resistance in the working 

 coils, the electro-magnets, and the external circuits of dynamo-electric 

 machines. In this paper he shows that in such a machine giving a 

 continuous current the equation E= ^/B, E' holds ; in which E is the re- 

 sistance of the external circuit and R E' are the resistances of the field- 

 magnets and the revolving bobbins. If r represent the ratio of the 



total work to the lost work, and e= the formular — l+2Ve results. 



Xv 



The dynamo considered in these calculations has its field maintained by 

 a shunt circuit. {Nature, September, 1881, xxiv, 52C; C E., September, 

 1881, p. 474; Am. J. Set., December, 1881, xxii, 484.) 



The Pacinnotti electro-magnetic machine, constructed in 18G0 and de- 

 scribed in 1864, has become interesting since the invention by Gramme 

 of his ring armature. This machine was exhibited at the electrical ex- 

 hibition in Paris, and the article from the Italian journal, in which it first 

 appeared, has been republished in several of the electrical journals. {11 

 Nuovo Cimcnto, June, 1864, xix, 378 ; VElectricien, November, 1881, ii, 127 ; 

 J. Phys., November, 1881, x, 461.) Another machine with a ring arma- 

 ture was exhibited in the Holland section as having been made by Elias 

 in 1842. But beside the ring armature in six sections, and the commu- 

 tator in six pieces, there is no correspondence between tliis and the 

 Gramme machine, the connections being made quite differently. {VElec- 

 tricicn, November, 1881, ii, 125.) 



