Induced Alternating Current Discharge. 71 



In a second* communication to the Royal Society, " On the 

 Spectrum of Water," Liveing and Dewar state that the spec- 

 trum which they had figured in the article just mentioned did 

 not by any means exhaust the spectra of flames observed by 

 them, but that it was as much as they were able at that time 

 to trace to water as its cause. In a thirclf article they give the 

 results of a very searching investigation of the spectrum of the 

 oxy-hydrogen flame. By making long exposures they obtained 

 photographs of the oxy-hydrogen flame, showing closely set lines 

 from wave lengths 2268 to ilOO, with traces of lines beyond 

 those limits. The whole spectrum appeared to consist of a 

 rythmical series of lines, the strongest of these series being the 

 one first described. 



Liveing and Dewar refer to an article^ by M. Deslandres in 

 which he states -that the first band of the water spectrum (i. e. 

 the group beginning at wave length about 3063) includes a 

 series of rays which reproduce, line for line, at the same dis- 

 tance and with the same relative intensities, the band A of the 

 solar spectrum ; and that the second band (i. e. the group 

 beginning at a wave length about 2811) includes a series cor- 

 responding to B, and that in the third a may be found to 

 be reproduced. Liveing and Dewar were not able to make 

 out such an exact correspondence between the lines of the 

 water spectrum and those of A, B, and a as M. Deslandres' 

 words seem to imply, but nevertheless the similarity of the 

 grouping was very remarkable. 



To study further the question whether these lines were due 

 to water vapor, or to the effect of water vapor upon the gases 

 occupying the intra-polar space, a plate was exposed to the 

 discharge when it took place under special conditions, namely 

 that the upper half of the plate should be exposed to the dis- 

 charge when it took place in ordinary air and the lower half 

 of the plate to it when it took place in air containing a large 

 amount of moisture. For the purpose of supplying a large 

 amount of water vapor to the air about the discharge during 

 the exposure of the lower half of the plate, water was boiled in a 

 glass flask, containing a cork stopper through which passed a 

 glass tube so shaped that by its means the issuing jet of steam 

 could be easily directed into the flame. 



In this experiment the upper half of the plate was exposed 

 for forty-five minutes to the discharge in ordinary air, and the 

 lower half for the same length of time when steam was sup- 

 plied to it. In the latter case the time during which the light 

 actually fell upon the slit of the spectroscope was not really as 



*Proc. Roy. Soc, vol.- xxxiii, p. 274. 

 \ Trans. Roy. Soc, vol. clxxix (A), p. 27. 

 % Comptes Rendus, vol. c, p. 854. 



