High Frequency Spectra. 



199 



same holder as S^. This holder was constructed to allow the 

 following adjustments: (a) It could be moved towards the axis 

 of rotation of the spectrometer; (b) Si could be made vertical; 



Figure 1a 



Figure. 1b 



DIAGRAM OF THE SPECTROMETER 



(c) the line joining the centres of the slits could be made to pass 

 through the axis of rotation. 



Rotation Apparatus. — The vernier circle was rotated by means 

 of a tangent screw. By means of a reduction gear, this was 

 turned at 1 /10,000th of the speed of a small motor. In the ex- 

 periments, the rate of rotation of the crystal was about 2° per 

 hour. 



