470 i >. \>. Livri 



hydrogen, ami yet it i- very difficult to obtain a photograph of it when 

 no gas but hydrogen is known to be present. or. at lea>t. to i>ec.>me 

 luininoiis in the electric di>clia:_ 



We have had an opportunity of comparing the <]>c-t!uni of the 

 volatile residue of air with that of the more volatile part of ga* from 

 the Bath spring. The tulie did not admit of the sejwirate examination 

 of the light from the negative pole, but was examined end-on, so that 

 the radiation probably included rays emitted from the neighbourhood 

 of the negative jxjle. The whole of the hydrogen had been removed 

 from the Bath gas, but not all the argon. In the spectrum of tl 

 the rays of helium are dominant, decidedly stronger than tho-.- ..f 

 neon, although the latter are very bright. In the sj>ectrum of the 

 : esjdue of atmospheric air, the proportion of helium to neon seems 

 reversed, for in this the yellow neon line is as much more brilliant than 

 the yellow helium line as the latter is the more brilliant in the sjH?ctnini 

 of Bath gas. All the prominent lines in the sjn-etrum of the volatile 

 residue of Hath gas were also in that of the residue of atmospheric 

 air, except the argon lines. There were, on the other hand, many lines 

 in the latter not traceable in the former, some of them rather con- 

 spicuous, such as the ray at about A 4(><>4. It is, of course, probable 

 that such rays are the outcome of some material not contained in the 

 Bath gas. A very conspicuous pair of lines appears in photographs of 

 the spectrum of the air residue, at about A .'55S7, which is not traceable 

 in the spectrum of Bath gas. The helium line, A .V7 -I. is seen in the 

 latter spectrum, but is quite obscure* 1 in the former spectrum by the 

 great intensity of the new pair. This helium ray is really a close 

 double, with the less refrangible continent much the weaker of the 

 two, but the new pair are wider ajwirt, and of nearly equal intensities ; 

 this < -haracter also distinguishes them from the strong argon line at 

 A 3588-6. They are, however, very much more intense at the negative 

 pole than in the capillary, and it will require a good deal more study 

 to determine whether these rays, and many others which we have not 

 tabulated, are due to the peculiarity of the stimulus at the negative 

 pole, or to the presence of a previously unrecognised material. 



A> our mixture of gases prolwibly includes some of all such gases as 

 pervade interplanetary ami interstellar space, we early looked in their 

 spectra for the prominent nebular, coronal, and auroral rays. Search- 

 ing the spectrum about A 5007 no indication of any ray of alnmt that 

 wave-length was visible in the spectrum of any one of the three tubes 

 which had leen tilled as al>ove descriled. Turning to the other 

 nebular line at alnmt A 4959, we found a weak rather diffuse line to 

 which our first measure a-ssigned a wave-length 4'.i"s. The correctness 

 of this wave-length was subsequently verified by measuring with a 

 micrometer eye-piece the distances of the line from the helium lines 

 A 4922'! and A 5015*7 which were in the field of view at the same 



