316 PROCEEDINGS OP THE AMERICAN ACADEMY. 



It is only too easy to obtain the bands in the region of short wave- 

 lengths, for, to quote Schumann himself, 4 they are "the unwelcome 

 attendants of all my spectra." In order to determine the cause of the 

 phenomenon, however, experiments were made with both carbon mon- 

 oxide and carbon dioxide and with a variety of conditions in the dis- 

 charge tube. The results of these experiments may be stated as fol- 

 lows : Exactly the same bands are obtained when carbon monoxide is 

 used as when carbon dioxide is employed, but in the former case the 

 strength of the whole spectrum is considerably greater than in the 

 latter. With increased current strength from a transformer, between 

 five and twenty milliamperes the intensity of the bands increases in 

 a uniform manner throughout the extent of the spectrum. When a 

 spark gap is placed in series with the tube and a condenser is intro- 

 duced in such a way as to produce a disruptive discharge, the spectrum 

 at first weakens and then vanishes altogether. The effect is accom- 

 panied by a very marked decrease in pressure in the tube and by the 

 formation of a dark deposit on the walls of the capillary. When 

 precautions are taken to exclude the introduction of carbon monoxide 

 or prevent its formation, the spectrum is greatly weakened if it does 

 not vanish altogether. 



These data go to confirm the results of Schumann, as they show that 

 the spectrum is due to carbon monoxide. The occurrence of the bands 

 when carbon dioxide is present may be explained by the fact that this 

 gas is known to be transformed into carbon monoxide under the influ- 

 ence of light and the electric discharge. 5 The disappearance of the 

 spectrum with the disruptive discharge is due to the destruction of 

 the carbon monoxide. The oxj^gen set free by the reaction seems to 

 combine with the electrodes, while the carbon is deposited. This 

 property of a condenser discharge is useful, since it permits the spec- 

 troscopist to free his apparatus of an annoying impurity. The decrease 

 in pressure which accompanies this reaction is often a striking and 

 important phenomenon. 



In making measurements in the region between A 1880 and A 2080 

 a concave grating of six foot radius with 15028 lines to the inch was 

 employed. Schumann plates were used throughout the work. For 

 the experiments in the region on the more refrangible side of A 1880 

 the writer's vacuum spectroscope was employed 6 in the same manner as 

 when the hydrogen spectrum was under investigation. An improve- 

 ment in the discharge tube, however, has been introduced. The nature 



4 Loc. cit., p. 16. 



6 Herchefinkel, Comptes Rendus, 1909, 149, 395. 



6 See note 2. 



