122 Prof. J. Zeleny on the Ratio of the Velocities of the 



for obtaining the two velocities separately has not yet been 

 devised. 



The method described below deals with the ratio of the two 

 velocities, which is the quantity under consideration. The 

 two actual velocities can, if desired, be obtained by means of 

 this ratio from the value of the sum. 



§ 1. The Method. 



The method employed for determining the ratio of the 

 velocities of the two ions is based on opposing a stream of 

 gas to the velocity due to the electric forces. 



Fi£. 1. 



A 



X> 



Ms 

 ■< "< 



B 



> 



Suppose A and B in fig. 1 to represent two plates made of 

 wire gauze, the space between which is exposed to Rontgen 

 rays. If the plates are connected to the opposite poles of a 

 battery C which maintains a potential-difference of U volts 

 between them, then if d is the distance between the plates in 

 centimetres, and we suppose for the present a uniform 

 potential gradient, the fall of potential between them is 



~j volts per centimetre. 



Under the action of this electric force the ions move in 

 opposite directions between the plates, and if u is the velocity 

 with which a positive ion moves and v that with which a 

 negative one moves when the potential gradient is one volt 

 per centimetre, then the velocities of the positive and negative 



u ■ u .. . 



ions are u— and v-j respectively. 



These velocities may be increased either by increasing U or 

 by decreasing d. 



