Fig. 9. 



Fig. 10. 



Fig. 11. 



Fig. 12. 



PLATE III. 



Fig. 9. — Enlargement of portion of track of beta particle emitted in air exposed 



to X-rays. 

 Fig. 10. — Separation of positive and negative ions by an electric field in air 



exposed to X-rays. 

 Fig. 11. —X-ray beam incident on thin copper plate. 

 Fig. 12. — X-ray beam incident on thin copper plate, the less penetrating rays 



having been intercepted before entering the cloud chamber. 



4S8J 



