1882.] Electric Discharge with Chloride of Silver Battery. 437 

 Alphabetical List of Reference Letters. 



All. Allantois. 



B.v. Blastodermic vesicle. 



c.v. Cellular layer derived from placental pole of blastodermic vesicle. 

 ep. Epiblast. 

 fa. False amnion cavity. 

 hy. Hypoblast. 

 i.a. Interamniotic space. 

 m. Mesoblast. 

 N.a. Neur-amniotic cavity. 

 p.p. Placental pole of blastodermic vesicle. 



VII. " On the Electric Discbarge with the Chloride of Silver 

 Battery." By Warren De La Rue, M.A., D.C.L., F.R.S., 

 and Hugo Muller, Ph.D., F.R.S. Received December 21, 

 1882. 



In anticipation of a paper to be shortly communicated to the Society, 

 we wish to state that we have found that the pressure of least resis- 

 tance for a given gas is not a constant, but that it varies with the 

 diameter, shape, and dimensions of the vessel employed. 



Moreover, that the dark space near the negative in electric dis- 

 charges in vacuum tubes is dark only by comparison ; for we have 

 obtained a photographic image of the dark discharge in a tube in which 

 the strata remained steady during forty-five minutes. The time of 

 exposure was fifteen and thirty-five minutes ; a comparison of the 

 latter result with a photograph obtained of the strata in two and a half 

 seconds shows that the dark space is 840 times less bright than a 

 stratum. 



Lastly, a tube with palladium terminals, which we made several 

 years ago, containing hydrogen gas, shows in a remarkable manner 

 the power of terminals to occlude gas and to give it off again. On 

 passing an electric discharge through this tube for a few seconds, it 

 becomes blackened, especially near the negative, by the deposit of a 

 mirror-like film ; on leaving the tube for few days' rest, this mirror 

 disappears entirely, and is reproduced by passing a fresh current. It 

 is most probably a volatile hydrogen alloy of palladium. The effects 

 described have been reproduced very many times during eight years. 



The Society adjourned over the Christmas Recess to Thursday, 

 January 11th, 1883. 



VOL. XXXIV. 



