( 290 ) 



spar are projected in die plane of (he slit of the spectroscope. The 

 two images could be examined separately. 



"Bei richtiger Stellung des Kalkspaths bestand das eine Bild aus 

 Licht, dessen elektrische Schwingungen in der Lichtquelle parallel 

 den Kraftlinien vor sich gehen, das andere Bild aus Licht, dessen 

 elektrische Schwingungen in der Lichtquelle aut' den Kraftlinien 

 senkrecht stehen. Dass die Ebene der Schwingungen nach dem 

 Durchsetzen des Kalkspaths durch «lie Quarzlinse gedreht wird, thut 

 nichts zur Sache". 



Bij means of this arrangement the components with vertical vibra- 

 tions are undoubtedly separated from those with horizontal ones. The 

 main object of Rünge and Paschen's investigation being the connexion 

 between series and magnetic separation there is no objection to be 

 made. The case is changed however as soon as the relative inten- 

 sities of the components in the emitted light are under investigation, 

 for these under certain circumstances could be essentially altered. If 

 vertical and horizontal vibrations are reflected differently by the 

 grating, the rotation of the direction of vibration in the beams 

 passing through the quartz lens of course will be apparent in the 

 observed intensity. 



Polarizing effects of gratings are well known and generally the 

 direction of vibrations relatively to the grooves must be of importance. 



I had not anticipated that this circumstance would give rise to 

 such striking effects as were observed by me in some experiments 

 with a large Rowland grating. 1 have only made some observations 

 with the yellow mercury lines, observing in the spectrum of the first 

 order. The incident rays made an angle of about 19° with the nor- 

 mal to the grating, and in this latter direction observations were 

 made or photographs taken. A vacuum tube charged with some 

 mercury ') was placed in the magnetic field and by means of a 

 glass lens an image was projected on the slit of the spectroscope. 

 The light emitted at right angles to the horizontal magnetic lines of 

 force was investigated. 



In figure 1. a reproduction is given of the triplet in which the 

 line 5769.4 is resolved. The distribution of intensities is in absofute 

 contradiction with equation (I). 



Observations with a calcspar and a sodium flame, the lighl of 

 which was incident on the grating at about the same angle as 

 above specified, the direction of observation being normal to the 

 grating, showed at once that the light reflected from the grating 



J) F. Paschen, Physik. Zeitschr. Jahrg. 1 p. 47<s. f900. 



