41129 
Physics. — “A method for obtaining narrow absorption lines of 
metallic vapours for investigations in strong magnetic fields.” 
By R. W. Woop and P. Zrrman. (Communicated by Prof. 
P. ZEEMAN). 
(Communicated in the meeting of January 25, 1913) 
In the summer of 1911 we intended to make together some 
observations concerning magnetic double refraction of metallic vapours. 
The magnetic double refraction of some vapours was first discovered 
(and predicted) by Vorer, afterwards commented upon by Zreman 
and GEEST. 
In the paper of the last named authors the interesting region 
between the components of the magnetically divided sodium lines 
was investigated and the results represented by drawings. 
It seemed desirable to extend this investigation using very narrow 
lines, which can be maintained constant during a long time and to 
fix the result by photograms. 
Our investigation never passed the preliminary stage and has 
become now superfluous by the paper of Vorer and Wagner which 
has since appeared. 
During our preliminary observations we tested a great number of 
methods of obtaining narrow and constant absorption lines. It seems 
to present some interest to record one of our results. 
The absorption lines of sodium were obtained beautifully narrow 
by using small glass tubes charged with a little metallic sodium, 
then sealed to the vacuum pump and evacuated. A tube some 
centimeters in length was placed vertically between the poles, the 
magnetic field being horizontal. 
It is quite possible to use tubes of an external width of some 
millimeters. Of course much of the light of an are lamp is reflected 
and diffused by the tube, but enough remains to observe the inverse 
magnetic effect with a large Rowvanp grating. The magnetic resolution 
of the narrow lines can be splendidly seen and photographed in a 
reasonable time. 
The heating of the tube can be done by a flame, but preferently 
electrically. 
Of course tubes with other volatile metals can be prepared in 
the same way '). 
1) The method has been since applied with success in an investigation by 
Mr. Wo rer in the Amsterdam laboratory; the results will be given separately. 
