﻿Oil the Ionization produced by Ttordgen Rays. 



115 



circular section, which at 100 cm. from the anode would he 

 of convenient breadth ; for this breadth determines the size 

 of the apparatus required to measure the ionization. At the 

 same time this beam had to contain enough rays to produce 

 a measurable ionization. The obvious method of producing 

 a cone of rays is to allow the rays to pass through a small 

 hole in a lead screen ; but preliminary experiments showed 

 that if the screen was near the anode, the beam was much 

 too large at 100 cm., while if far off (of course it could not 

 be more than 30 cm.), the ionization was not measurable 

 unless the ions were multiplied by collision, a matter of some 

 difficulty and inconvenience. For these reasons the idea ol 

 working with rays diverging from a very small area was 

 abandoned. 



The other points requiring attention were the elimination 

 of absorption by the air, and to guard against accidental 

 variations in the Rontgen ray bulb. 



As a result of these considerations, the apparatus took the 

 form shown in fig. 1. Other things being equal, the ionization 

 can be made large by using a powerful bulb, and the one at 

 hand happened also to be of the very convenient shape shown 

 in the figure. 



SO Velta 



To Euctxcmzte* 



ELTCTSeMETER 



The bulb and induction-coil were contained in a lead box 

 with a window near the anode ; the primary current, which 

 had a mean value of about 4 amperes, was taken from the 

 town mains (100 volts) through a rough resistance and a 

 Rotax interrupter to the coil, and the voltage across the coil 



I 2 



