Secondary JL-rays and Electromagnetic Pulse 7 heory. 



273 



The ionization chamber (fig. 2) wag cylindrical in shape, 

 6 cm. Ions and 2'3 cm. in diameter, with an axial electrode, 



Fis. 2. 



one end of which passed through an insulating plug into the 

 o-old-leaf electroscope, where contact was made with the gold- 

 leaf system. At the other end the cylinder projected beyond 

 the ionization chamber itself, so as to limit the obliquity of 

 rays entering the ionization vessel. By means of slide tubes 

 the length of the protecting tube could be varied to suit each 

 particular experiment. The outer end of the ionization 

 chamber was of thin aluminium and the inner end of lead. 

 Inlet and outlet tubes were provided for this chamber. The 

 sensitiveness of the arrangement was greatly increased by 

 using air saturated at 0° C. with methyl iodide as the gas to 

 be ionized. It was thought that this would be preferable 

 to the tilted electroscope as it was necessary to move the 

 whole system frequently. 



The ionization chamber, electroscope, and observing micro- 

 scope were placed on a small wooden table at the end of an 

 arm which was capable of rotating round a vertical axis. 

 The axis of the ionization chamber was horizontal and radial, 

 the end of the chamber being about 15 centimetres from the 

 centre of the carbon. This distance was varied slightly for 

 different experiments^ 



A square slab of carbon 8 cm. x 8 cm. X *8 cm. was held in 

 a vertical plane, with its centre on the axis of rotation of the 

 apparatus, and approximately on the axis of the ionization 

 chamber. The carbon also was capable of rotation round the 

 same vertical axis. 



A beam of X-rays rectangular in section was directed 

 horizontally on to the carbon plate. The intensities of 

 secondary radiation proceeding in two directions making- 

 equal angles with the normal to the plate were compared by 

 observing the rates of deflexion of the gold-leaf when the 

 axis of the ionization chamber was in the corresponding 



Phil Mag. S. 6. Vol. 21. No. 122. Feb. 1911. T 



