Volatile Gases of Atmospheric Air. 155 



described, — (the U-tube in liquid bj Nojes having been dis- 

 pensed with) was pumped out and examined. This mixture 

 was found to contain 43 per cent of hydrogen, 6 per cent of 

 oxygen, and 51 per cent of other gases — nitrogen, argon, neon, 

 helium, etc. — and it was explosive when mixed with more 

 oxygen. This shows conclusively that hydrogen in sensible 

 proportion exists in the earth's atmosphere, and if the earth 

 cannot retain hydrogen or originate it, then there must be a 

 continued accession of hydrogen to the atmosphere (from inter- 

 planetary space), and we can hardly resist the conclusion that a 

 similar interchange of other gases also must take place. The 

 tubes containing the residue of atmospheric gases uncondensed 

 at the temperature of liquid hydrogen we have examined 

 spectroscopically. 



On passing electric discharges through them, without any 

 condenser in the circuit, they glow with a bright orange light, 

 not only in the capillary part, but also at the poles, and at the 

 negative pole in particular. The spectroscope shows that this 

 light consists in the visible part of the spectrum chiefly of a 

 succession of strong rays in the red, orange, and yellow, 

 attributed to hydrogen, helium, and neon. Besides these, a 

 vast number of rays, generally less brilliant, are distributed 

 through the whole length of the visible spectrum. They are 

 obscured in the spectrum of the capillary part of the tube by 

 the greater strength of the second spectrum of hydrogen, but 

 are easily seen in the spectrum of the negative pole, which 

 does not include the second spectrum of hydrogen, or only 

 faint traces of it. Putting a Leyden jar in the circuit, while 

 it more or less completely obliterates the second spectrum of 

 hydrogen, also has a similar effect on the greater part of these 

 other rays of, as yet, unknown origin. The violet and ultra- 

 violet part of the spectrum seems to rival in strength that of 

 the red and yellow rays, if we may judge of it by the intensity 

 of its impressions on photographic plates. We were surprised 

 to find how vivid these impressions are up to a wave-length 

 314, notwithstanding the opacity of glass for rays in that part 

 of the spectrum. The photographs were taken with a quartz- 

 calcite train, but the rays had to pass through the glass of the 

 tube containing the gases. 



We have made approximate measurements of the wave- 

 lengths of all the rays which are sufficiently strong to be seen 

 easily or photographed with an exposure of thirty minutes, and 

 give a list of them below. These wave-lengths are computed 

 to Rowland's scale, and were deduced from the deviations pro- 

 duced by two prisms of white flint glass for the visible, and of 

 calcite i'or the invisible, rays. The wave-lengths assigned to 

 the helium lines are those given by Runge and Paschen, and 



