A. C. REDFIELD AND E. M. BRIGHT 39 



In order to calibrate the "spectrum" of |8-rays the apparatus was 

 modified as shown in Fig. 4. To make more room the water jacket 

 was removed from the interior of the solenoid, and a brass tube ar- 

 ranged to extend into the center of the coil and support a small ioni- 



FiG. 4. Diagram of arrangement used to determine the relative ionizing powers 

 of homogeneous groups of /3-rays to different velocities. 



zation chamber, I. The roof of this chamber consisted of a lead 

 plate 3 mm. thick which prevented any /3-rays from entering the 

 chamber except through a hole, 0, 1 mm. wide and 1 cm. long. The 

 lead blocks which supported the tube of radium emanation rested 



