Precision-measurements in the X-Ray Spectra. 603 



To separate the high vacuum in the X-ray tube from the 

 low vacuum in the spectrograph a gold-beaters' skin with 

 red paper, an aluminium foil or some other foil was pressed 

 over the slit. 



Fig. % 



Great care was taken to obtain an accurate adjustment of 

 slit, crystal, and plate, for which purpose special apparatus 

 were constructed and built. 



A great deal of the work has been devoted to the con- 

 struction of an effective X-ray tube for spectral purposes in 



2T2 



