729 



o 



sodium lines would aiiioiuit to 0.17 A.U.; in this case the differ®'^^^ 

 of the intensities was therefore a maximum at a distance of tiie 



o 



Zeem AM-com ponen ts or on an average 0.34 A.Ü. 



Now on closer consideration it is clear that the correct interpreta- 

 tion of Miss V. Ubisch's observations would be very intricate, 

 and many more data would have to be available for it. In the 

 tirst place we should have to know the cori-ect distances and 

 intensities of the ZEEMAN-components, before thej undergo absorption 

 in the Wood tube; further the accurate course of the curve that 

 denotes the connection between the intensity of the light transmitted 

 in this tube with the wave length, shoukl be known. The absorption 

 maxima of sodium vapour not being sharply defined lines, much 

 will depend on the intensity and sharpness of these maxima; this 

 is the more obvious when it is borne in mind that the real maxi- 

 mum difference of intensity observed by Miss v. Ubisch, constitutes 

 only a few percentages of the whole amount. With so small a 

 difference we should be sooner inclined to assume a differerice 

 in absorption to that amount than as the author does, suppose 

 that one ZEEMAN-component is not weakened at all, the other 

 only a few percentages in the case of a thickness of layer which 

 is at any rate pretty considerable. It is easy to imagine cases in 

 which the absorption maxima are of equal intensity, but difference 

 of intensity of the ZEEMAN-components is a maximum, when they lie 

 outside the absorption maxima. 



Everything considered the amount given by the author can only 

 represent the distance of the absorption maxima as far as the order 

 of magnitude is concerned; accordingly I do not think that the 

 result of my observations (distance of the absorption maxima of 



o 



about 0.15 A.U. at 270°) is in contradiction with that of Miss v. 

 Ubisch. 



Besides it is possible that the temperature has not been given 

 perfectly accurat.-ly. In this respect a Woou tube presents more 

 sources of errors than the uniformly heated tube which I used. 

 Moreover the ditforeiice need not be very great, taking the very 

 rapid increase of the resolution in the neighbourhood of 300° into 

 consideration. 



When seeking an explanation of the observed phenomena now that 

 it has appeared that in the tirst place there is here question of a 

 density effect, we are naturally led to look for a connection with 

 the widening of spectrum lines in general, and with the explanation 

 which Stark has given for it, which comes to this that this widening 



