252 



ME. E. M. WELLISCH ON THE MOBILITIES OF THE 



of curve actually obtained by experiment ; it was obtained under the following 

 conditions : 



Gas between electrodes, carbon monoxide at 1 atmosphere. 

 X (before reversal) = 387 volts per centimetre. 

 Distance between electrodes, 1 cm. 



T/Mt 



/A/ SECl /VOS 



024 



Fig. 3. 



In general, only two points of discontinuous curvature are noticeable, the first 

 corresponding to the Rontgen ray discharge and the second to the withdrawal of all 

 the ions of one sign, viz., the negative ions if B be at a positive potential before 

 reversal and the positive ions if B be at a negative potential before reversal. By 

 obtaining experimentally curves for the two cases of B positive before reversal and 

 B negative before reversal, we will thus be able to find the negative and positive 

 mobilities respectively. 



Taking the case represented in fig. 3, suppose the plate A is connected electrically 

 with a similar plate A', whose position with respect to the Rontgen-ray bulb is so 

 adjusted that it receives after each discharge a quantity of electricity represented 

 graphically by the straight line ABC in the figure. Thus, considering the quantity 

 jointly received by the plates A and A', the relation between Q and t will be repre- 

 sented by the curve DOE, whose ordinates are obtained by adding those of the two 

 curves ABC, LPM ; in other words, as long as t is negative there is, on the whole, no 



