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XXXVI. The High-Frequency Spectrum of Tungsten. By 

 James Barnes, Ph.D., Research Fellow, University of 

 Manchester *. 



fllHE investigation of the high-frequency spectrum of the 

 -L X rays coining from a Coolidge tube with a tungsten 

 anticathode was thought to be of interest in connexion with 

 the accompanying paper f. The method used for obtaining 

 and photographing the spectrum was the same as that 

 employed by Moseley J. The crystal was placed on a 

 goniometer table and adjusted so that the face upon which 

 the rays were incident passed through the axis of rotation. 

 The beam of rays coining through the slit of about 0*5 mm. 

 width was intersected by the axis and fell approximately on 

 the centre of the face of the crystal. The perpendicular 

 distance from the axis to the photographic plate was 

 20'12 cm., and the distance from the siit to the axis was 

 made as near as possible the same. The crystal was kept 

 throughout the exposure in slow rotation by the method 

 used by Professor Rutherford and Dr. Andrade § in their 

 determination of the spectrum of the soft gamma rays from 

 radium B. 



The lines were first photographed on one side of the 

 central image of the slit, then the crystal was turned 

 through 180° and the lines obtained on the other side. The 

 so-called reflexion angle 6 can then be calculated from the 

 expression 



2<9=tan- 1 



40-24' 



where a is the distance between like lines on the same plate. 

 The longest time of exposure employed was six hours. 

 Satisfactory photographs of the strongest lines in the " L " 

 series could easily be got in half an hour. The glass wall of 

 the bulb being 0'5 mm. thick, at least one-fiftieth of the 

 intensity of this soft radiation is absorbed by the glass. 

 With a bulb having a side tube with its end covered with 

 thin aluminium, good photographs of this series would 

 probably be obtained in a few minutes under similar 

 conditions. 



The following table contains the results obtained with a 

 rock-salt crystal, 1*6 cm. thick, whose face was 3*5 x 1*9 cm. 



* Communicated by Sir Ernest Rutherford, F.R.S. 



t Phil. Mag. supra, p. 339. 



+ Phil. Mag. xxvii. p. 703 (1914). 



§ Phil. Mag. xxvii. p. 858 (1914). 



