Mr Whiddmgton, Note on the Velocity of X-ray Electrons 443 



were obtained after considerable difficulty, but the method was 

 abandoned since it was found that in spite of all precautions the 

 thin foil rapidly disintegrated, wearing thin and eventually breaking. 

 The apparatus finally adopted is shown in the figure. 



Cathode-rays from the concave cathode C are focussed on the 

 water-cooled target T. Immediately below T is the fine sht S 

 (•5 mm. wide and 5 mm. long). About 2 cm. below this slit is 

 another wider slit leading the rays into the evacuated box B on the 

 under surface of which a photographic film F can be placed. The 

 collimator projects a little spot of light on the film for reference 

 purposes. The whole system of X-ray bulb and camera is evacuated 

 by a hquid air charcoal bulb F. 



At right angles to the plane of the figure a nearly uniform 

 magnetic field is applied so that the X-ray electrons streaming into 

 the box are focussed on the film. This method was originally used 

 by Rutherford for the determination of the speed of j8-rays, was 

 later used by Rawlinson and Robinson* in an experiment on X-ray 

 electrons and was also used by de Broghe| in the experiments just 

 cited. 



Under good conditions as much as five milliamperes can be 

 passed through the bulb and it is interesting to compare the 

 efficiency of the arrangement above illustrated with that of de 

 Broglie using a Coolidge tube. 



* Phil. Mag. 1913. 



t Loc. cit. 



