Dr. J. A. Crowther on U J " Radiation. 



721 



of judgment, is not one which can be maintained in the face 

 of experimental facts. The former, and more vital, objection 

 it is hoped that the results described in the present paper 

 may do something to remove. 



Experimental Details. 

 The apparatus employed was similar to that already used 

 for investigating the distribution of the scattered radiation 

 round a radiator and described in previous papers (J. A. 

 Crowther, locc. citt.). The radiator was mounted on an 

 aluminium frame carrying a pointer moving over a circular 

 graduated scale, so that it could be set at any desired angle 

 with the primary beam. The primary beam issuing from a 

 large water-cooled tube of fine focus F (fig. 1), was confined 



Fiff. 1. 



to a narrow rectangular pencil by a series of lead screens. 

 Two ionization chambers C p and S of the same size and 

 pattern were used for measuring the radiations. These were 

 mounted on a circular geometrical slide, the centre of the 

 circle being immediately below the radiator. The chambers 

 could thus be set at any desired angle with the primary 

 beam, without altering their distance from the radiator. 

 Before reaching the radiator the primary beam passed 

 through an ionization chamber A, consisting of a pair of 

 parallel plates between which the beam passed without 

 impinging on either. This enabled the initial intensity of 

 the primary radiation to be measured. Each ionization 

 chamber was connected to a separate electroscope oi' the 

 Wilson pattern. 



