between Anode and Kathode Spectra. 343 



not strong but fairly well seen. At first the spectrum shewed 

 lines of hydrogen as well as sodium, and the positive column 

 shewed striation, but these disappeared when the hydrogen had 

 been well pumped out. The light about the kathode then 

 shewed only the. D lines of sodium and a trace of the pair in 

 the citron at about A 568, while the bright column shewed in 

 addition the pairs in the green and blue at about A 515 and 498. 

 The head of the bright column was concave to the kathode and 

 was really the negative glow, separated from the kathode by 

 a relatively dark space in which the spectrum was weak. There 

 was no break in the column, and it was about equally bright 

 quite up to the anode and gave the same spectrum throughout. 

 At a somewhat higher pressure of vapour the light about the 

 kathode, and throughout the column, gave brightly, besides D, 

 the pairs at about the wave-lengths 616, 568, 515, 498, 475, and 

 466. They were identified by comparison with the spectrum of 

 the spark in air between two beads of sodium carbonate. The 

 fragments of solid sodium, or rather the skin of oxide they had 

 acquired before the tube was pumped out, fluoresced brilliantly 

 in the kathode rays with an emerald green light, which however 

 gave only a continuous spectrum. 



With cadmium vapour, when all carbon dioxide had been 

 pumped out, there was no striation. The spectrum was the same 

 in all parts of the tube, and shewed the characteristic triplet, 

 about A 5085, 4799, 4677, the orange line about A 6438, and the 

 green line about A, 5153. At the kathode, when the vapour 

 pressure was not too low, there appeared in addition the two 

 green lines about A. 5378, 5337, and the indigo blue line about 

 A, 4415, usually seen only with a jar discharge in the spark 

 between cadmium electrodes in air. As these three lines were 

 not observed at the anode it may be supposed that they belong 

 exclusively to the kathode glow. I think, however, that as they 

 are seen only at higher pressure when the absorption of the 

 kathode rays is most rapid and the consequent intensity of the 

 glow greatest, their appearance is a question of relative intensity, 

 and they are not part of a different spectrum. 



In thallium vapour there was a good negative glow which 

 shewed the green thallium line only. The anode shewed the 

 same. The whole tube was filled with a green glow, unstriated. 



In this respect all the metals examined behaved alike. 



Turning to compound gases. Hydrochloric acid gives no 

 spectrum which I can ascribe to the undecomposed molecules. It 

 gives, in a tube with platinum electrodes, a good kathode glow 

 with a spectrum which consists of the lines of chlorine and the 

 first spectrum of hydrogen, and nothing else that I can detect. 

 The capillary shews in addition a continuous spectrum in the 



