374 



De La Rue and Muller. 



[May 16, 



May 16, 1878. 



Sir JOSEPH HOOKER, K.C.S.I., in the Chair, 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. "Experimental Researches on the Electric Discharge with 

 the Chloride of Silver Battery. Part II. The Discharge 

 in Exhausted Tubes." By Warren De La Rue, M.A., 

 D.C.L., F.R.S., and Hugo W. Muller, Ph.D., F.R.S. Re- 

 ceived April 10, 1878. 



(Abstract.) 



We cannot flatter ourselves that we have done more during our 

 three and a half years' work than contribute a few facts towards the 

 data necessary for the solution of the problem of the cause of stratifi- 

 cation produced by the electric discharge in vacuum tubes. We refrain 

 for the present from suggesting any hypothesis to account for this 

 beautiful phenomenon, in the hope of being able to confirm, experi- 

 mentally, certain views which we entertain concerning it. The paper 

 we have now the honour of laying before the Society consists mainly 

 of a record of the various appearances presented by the discharge in 

 residual gases at various pressures and with various currents. 



Throughout our labours we have felt strongly the necessity for 

 obtaining measurements of the physical conditions (nature and 

 pressure of the gas, strength of the current, difference of potentials 

 between the electrodes, size of the tubes, forms of electrodes) which 

 accompany the various phenomena observed during our experiments. 



In order that others may be in a position to theorize as well as 

 ourselves, we have given a more detailed account than we otherwise 

 should have done of the phenomena observed, which, for the same 

 reason, we have illustrated by copious diagrams and many copies of 

 photographs. 



For example, in diagram, fig. 43 are shown some of the very great 

 variety of phases in rarefied hydrogen, observed with tube 129, 32 

 inches long, 1 '6 inch diameter; the terminals being a straight wire 

 and a ring about 1 inch in diameter, both aluminium. We quote a 

 few observations by way of illustration : — 



Pressure 16 millims., 21,053 |VI (millionths of an atmosphere), 

 8,040 cells. The ring being positive, curiously formed luminous en- 

 tities shot at intervals from it, remained stationary for a time, and 



