292 Intelligence and Miscellaneous Articles. 



means be very conveniently measured. It is only necessary to 

 measure the deflexion in the electrometer connected with the plate 

 after it has been put to earth for an instant while ultra-violet rays 

 have been allowed to fall on the plate through the net. The light 

 of a zinc-carbon arc-lamp was always used. The plates of ordinary 

 metal and carbon were in air, or in a bell-jar filled with gases or 

 moist air. The net was of zinc, brass, or platinum. From the 

 differences of the observations with the same net and different 

 plates the differences of potential between the latter can be de- 

 duced. In dry and moist air and in carbonic acid they are the 

 same ; in hydrogen they are so for 0, Bi, Sn, Cu, Zn, but different 

 for Pt, Pd, ISTi, Pe. When hydrogen is gradually allowed to enter, 

 these metals behave as if they were gradually oxidizable in air. 

 Por platinum against a zinc net the difference of potential reduces 

 from 1*12 in air to 069 in hydrogen. On the fresh addition of 

 air the electromotive force returns in the opposite direction to its- 

 original value. Metals such even as tin and bismuth behave in am- 

 moniacal air as if they were less oxidizable, and therefore the opposite 

 of what obtains with hydrogen. Here also in air the initial electro- 

 motive force is restored. In coal-gas, carbon, copper, and platinum 

 behave like oxidizable metals. "With a platinum net and a copper 

 plate the sign of the electromotive contact-force is changed when 

 coal-gas is admitted instead of air. — Rendie. Lincei [5] p. 860, 1889 ; 

 Beibldtter der Pliysih, xiv. p. 69. 



MR. ENRIGHT S EXPERIMENTS. 

 To the Editors of the Philosophical Magazine and Journal, 



GrENTLEMES", 



When Mr. Enright described his attempts to prove that 

 contact could electrify hydrogen, in ' Nature,' August 18, 1887, I 

 wrote to that Journal (vol. xxxvi. p. 412) to point out that all 

 he had observed could be expressed in a few lines as due to the 

 well-known frictional electrification of spray. The length of his 

 communication to the Physical Society, printed in your January 

 number, may perhaps have deterred a critic from reading it. But 

 he makes no serious attempt to meet my obvious objection, and 

 so far as experiments so crude can negative anything they negative 

 his own contention. 



Tours faithfully, 



Olives, J. Lodge. 

 Liverpool, February 15, 1890. 



