710 Prof. R. W. Wood on a JSew 



weaker. These were found to be identical with the so-called 

 "water bands " of the oxy-hydrogen flame, as is clearly 

 brought out by fig. 9, in which the upper spectrum is that 

 of the oxy-hydrogen flame, the lower that of the emission. 

 In addition to these bands I obtained on one plate lines at 

 wave-lengths 3576, 3537, and 3369, which are identical with 

 lines attributed to nitrogen in the spectrograms published 

 by Eder and Valenta of the spark between wet carbon 

 electrodes. There is, in addition, a line which is imbedded 

 in the water-band, as shown in figs. 7 and 8. In fig. 7 the 

 upper spectrum is that of the oxy-hydrogen flame (over- 

 exposed), below it the aluminium spark, and at the bottom 

 the spark emission. The nitrogen lines come out very clearly 

 in this case. The spectrum by Eder and Valenta, which is 

 practically identical with that of the emission, was obtained 

 by passing the discharge of an induction-coil between wet 

 carbon electrodes, and differs from that of the oxy-hydrogen 

 flame in that it shows the nitrogen lines above referred to. 



It looked very much as if the emission might be due to 

 the fluorescence of nitrogen and water vapour, resulting 

 from the absorption of the Schumann waves ; this would 

 explain its failure to penetrate the air to any considerable 

 distance. To test this point the auxiliary tube was attached 

 to the spark chamber, the emission being studied through 

 the quartz window attached to the tube G. The apparatus 

 was first filled with air carefully dried by passage through a 

 tube filled with phosphorus pentoxide, and then with air 

 passed through a plug of w r et cotton. The emission was 

 photographed in each case, but no difference in the intensity 

 of the images could be detected. Oxygen and nitrogen were 

 then tried in succession. In the former there was almost no 

 trace of the emission, while in the latter it was much brighter 

 and extended to a greater distance from the aperture than 

 in air. Photographs of the phenomenon in these two gases 

 are reproduced on PI. XIV. fig. 4. The emission is photo- 

 graphed against the very black background furnished by the 

 long tube H, in fig. 1. The time of exposure was the same 

 in each case, and the two plates were developed together. 

 The aperture is to the right in each picture, the emission 

 shooting out towards the left. The crescent of light is the 

 inner edge of the tube H illuminated by diffused light. 



The next question was to determine whether the presence 

 of oxygen prevented the formation of the emission, or 

 whether the gas exerted an absorbing action. This was a 

 difficult matter to determine, since numerous experiments 

 showed that no substance was transparent to the emission. 



