168 



Prof. E. W. Wood. 



radiophone experiment I observed what appeared to be a lateral radia- 

 tion of a clear green light by the vapour. 



My first thought was that it was light scattered by the small 

 particles of oxide which are always floating about. If this were 

 case the spectrum of the light should be that of white light after trans- 

 mission through sodium vapour. An examination with the spectro- 

 scope, however, showed that this was not the case, for the spectrum 

 consisted of a diffused red band, a very narrow bright band in the 

 case where the D lines occur, and a diffused band in the green, in 

 which flutings seemed to be present. The general appearance of the 

 light reminds one of the fluorescence of uranium glass. 



I am at the present time engaged in an investigation of the spectrum 

 of this fluorescent light, but am not yet prepared to say whether the 

 flutings in the green are discontinuities in the emission or due to the 

 absorption of the non-luminous vapour surrounding the fluorescent 

 vapour. A careful photographic study will be necessary before this 

 can be decided, for which investigation I am employing an iron tube 

 provided with copper jackets at each end, through which water circu- 

 lates. (Fig. 7.) The light emitted laterally is observed through a 

 second iron tube inserted at a right angle, and provided with a glass 

 window. The sodium is placed at the junction of the tubes, which is 

 then raised to a red heat with a blast lamp. 



FIG. 7. 



So far as I am able to judge by passing the light causing the 

 fluorescence through colour screens, the wave-length of the emitted 

 light corresponds very nearly to that of the exciting vibrations. 

 Interposing a thin cyanine screen, which removes the light in the 

 neighbourhood of the D lines, causes no apparent diminution in the 

 intensity of the emitted light; but the spectroscope shows that the 

 bright band at wave-length 5890 has disappeared. A film stained 

 with aurantia, which removes everything below the " b " group, 

 greatly diminishes the intensity of the fluorescent light, and changes 

 its colour to red. A solution of cuprammonium of moderate strength 

 removes from the light all of the wave-lengths which are capable of 

 exciting the fluorescence. A more careful investigation will be neces- 



