﻿120 On the Ionization produced by Itontgen Bays. 



Discussion of Results. 



Taking into account all the possible errors, it seems that 

 the above result shows that the ionization in 1*5 cm. of a 

 beam 24 cm. from anode is almost exactly the same as at 

 98 cm. from anode, and the mean distances of these portions 

 are approximately 1 : 4. 



Even if the rays all diverged from a point on the anode, 

 this would mean tliat the number of ions produced by rays 

 of intensity I acting on air of volume Y is the same as 



those produced bv intensity — -, on volume 1GV. 

 i „ 'lb 



The discussion of the form of the beam shows that the 

 fjictor 16 should probably be much larger. 



Now, as pointed out at the beginning, this result is in 

 perfect agreement with the corpuscular theory; and in the 

 present state of our knowledge will also satisfy the pulse 

 theory, merely leading to the fact that the number of ions 

 produced in unit volume is proportional to the intensity. 



Any conception, however, of the action of an electro- 

 magnetic pulse in forming ions from a neutral molecule 

 must eventually result in the notion of the ions being torn 

 out of the molecules by the forces in the pulse, certain 

 molecules being at the instant in a more favourable condition 

 for this than others, as only a small proportion are ionized, 

 and obviously a certain minimum force is necessary for this ; 

 at the best, then, the inverse square law can only hold up to 

 a certain distance, and for large distance there should be a 

 rapid falling off from this law. In the experiments described 

 the square of the force in the pulse was diminished to at least 

 one sixteentli of its maximum value without an appreciable 

 change in the number of ions produced in the beam. 



The question really resolves itself into whether the minimum 

 force required to produce ionization on the pulse theory has 

 been approached in this experiment ; and in this connexion 

 the experiments of I. 0. Griffii h * are of interest. He studied 

 the ionization produced by ultra-violet light falling upon a 

 zinc plate which, if the pulse theory be true, must be much 

 the same sort of action as that of the Rontgen rays producing 

 ions in a gas. Taking tho«e of his distances which corre- 

 spond most closely to the 24 and 98 cm. of this experiment, 

 he found that if E represent the number of ions produced in 

 certain arbitrary units by light of intens-ity I on unit area of 



* Phil. Mag. xiv. p. 207 (1907). 



