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Physics. — ''On the Mmctare of the nhsoridlon Ihies D, amt D./'. 

 By Dr. G. J. Elias. (Coniinmiicatcd Uy Prol". H. A. Lorkntz). 



(Communicated in the meeting of April :24, 1914). 



Some time ago Prof. H. A. Lorkktz drew my attention to the 

 resnlts of an investigation by Miss G. v. Ubisoh '). From phenomena 

 observed by the writer during the investigation of the polarisation 

 state of light emitted by a sodium tlame in a magnetic Held after 

 it had passed through a tube filled with absorbing sodium vapour, 

 she infers that the wave length for which the absorption of the 

 vapour is a maximum, depends on its temperature, and in such a 

 way too that on rise of temperature a displacement towards the 



* o 



red takes place. The amount of this at 270'' would be about 0.17 A. U. 

 with respect to the emission line. It seemed worth while to ascertain 

 this result by direct observation. During the sumnier months of last 

 year ])r. W. J. dk Haas and myself occupied ourselves with this question. 



At first we intended to use an echelon-spectroscope for these researches, 

 observe by the aid of this the spectrum of a monochromatic source 

 of light, and then superpose the al)sorptioii lines of sodium vapour 

 on this. This vapour was in an iron tiil)e, closed on both ends by 

 plates of selected plate glass, and provided with water cooling; in 

 the middle the tube, which coj)tained there a vessel of metallic 

 sodium, could be heated. Such tubes were used by R. W. Wood 

 for the investigation of fluorescence of sodium vapour. First a blow- 

 flame served as monochromatic source of light, which was blown 

 by means of air in which a very finely divided solution (mist) of 

 soda was suspended. Aftei-wards the flame of a Méker-burner was 

 preferred, burning in an atmosphere in which a mist of soda was 

 also suspended. This was reached by placing the flame inside an iron 

 exit tube, at the bottom of which a reservoir was attached, which 

 was in communication with the air, and into which the soda-mist 

 was blown by means of an aspirator. This method appeared very 

 efficient to obtain a sodium flame of constant intensity, which is 

 moreover easy to regulate. 



The lines obtained by means of this source of light, were too 

 broad for the investigation with the echelon-spectroscope when the 

 intensity of the light was sufficient for the observation, the self- 

 reversal moreover being very troublesome then. If on the other 

 hand, the light intensity was diminished till the lines were narrow 

 guough, the intensity was again too slight for the observation. 



1) G. V. ÜBISCU. Inaug. Diss. Slrassbuig. 1^11. Ann. d. Phys. 35. p. 790; lull. 



