Volatile Gases of Atmospheric Air. 159 



equally strong, argon rays in the same region of the spectrum 

 were not absent from the aurora. Nor have we found in the 

 spectrum of our tubes any line with the wave-length 3915, 

 which is that of another strong auroral line. On the other 

 hand it seems probable that the strong auroral line, X 358, may 

 be due to the material which gives us the very remarkable pair 

 of lines at about the place of N of the solar spectrum, \ 3587, 

 which are very strong in the spectrum of the negative pole, 

 but only faint in that of the capillary part of our tubes. It 

 may well be that the auroral discharge is analogous to that 

 about the negative pole. We have also a fairly strong ray at 

 X 3700, which may be compared to the remaining strong ray 

 observed in the aurora A, 3700. This, however, is a ray which 

 is emitted from the capillary part of our tubes as well as from 

 the negative pole, and is, moreover, emitted by Bath gas, and 

 may very likely be a neon ray. 



We hope to pursue the investigation of this interesting 

 spectrum, and if possible to sort out the rays which may be 

 ascribed to substances such as neon and those which are due to 

 one or more other substances. The gas from Bath, even if 

 primarily derived from the atmosphere — which is by no means 

 sure — seems to have undergone some sifting which has affected 

 the relative proportions of helium and neon, and a more thor- 

 ough comparison of its spectrum with that of the residual 

 atmospheric gases may probably lead to some disentanglement 

 of the rays which originate from different materials. The 

 arrangement of the rays in series, if that could be done, would 

 be a step in the same direction. 



We are indebted to Mr. Robert Lennox, F.C.S., for the 

 great help he gave us in the complicated manipulation with 

 liquid hydrogen required to fill the spectral tubes, and to Mr. 

 J. W. Heath, F.C.S., for kind assistance. 



List of Approximate Wave-lengths of the Rays, Visible and 

 Ultra-violet, observed about the Negative Pole. 



The rays of hydrogen and helium, and those attributed to 

 neon by other observers are indicated by the chemical symbols 

 of those substances : 



A "b" prefixed to the number expressing the wave-length 

 indicates that the ray is emitted by gas from the Bath spring 

 as well as by that obtained from the atmosphere. 



A " c " similarly prefixed indicates that the ray has been 

 observed to be emitted from the capillary part of the tube as 

 well as from about the negative pole. 



A " w " indicates a weak line ; " s " a strong one ; " d " a 

 diffuse one ; " vw " a very weak ; and " vs" a very strong one. 



