Two Ions produced in Gases by Uontgen Radiation. 153 



It is seen that the chief difference between the two gra- 

 dients in the two cases is that when the negative ions are 

 moving against the stream there is a proportionally greater 

 fall of potential near the charged plate than for the similar 

 case with the positive ions. 



The change from the straight gradient is due to the excess 

 of the ions moving towards the charged plate, and this excess 

 is greater for the slower-moving positive ions than for the 

 negative ones; and in both cases, for the same reason, the fall 

 at the charged plate is less than when the air is at rest. 



Near the plate from which the blast is coming, the curves 

 are necessarily almost similar, from the nature of the con- 

 dition that brings the same amount of the two ions to the 

 gauze in the two cases. Since the ratio of the electric forces 

 acting in the two cases is actually found from the figures to 

 be nearly constant for points extending almost to the centre, 

 and as this includes the most efficient part of the field, it is 

 not necessary for our purpose to decide just how far out from 

 the gauze the forces influence practically the number of ions 

 that reach the gauze. 



The ratio obtained for the two gradients at these places is 

 nearly, but not quite, equal to the ratio of the potential values 

 used, and the difference is mainly due to the greater fall of 

 potential at the charged plate when the negative ions are 

 moving against the stream, as this leaves proportionally less 

 to be distributed in that case over the remainder of the space. 

 The correction calculated from the figures for air amounts to 

 about 2 per cent., which is to be added to the ratio of the 

 positive potential used to that of the negative ; and as this 

 correction is chiefly due to the difference of velocity of the 

 ions, the value obtained for air has been applied to the other 

 gases in proportion to the difference of velocity obtained for 

 them. 



§12. Remarks. 



From the table on p. 132, § 4, it is seen that for all of the 

 gases tried, where a difference of velocity for the two ions 

 exists, with one possible slight exception, the velocity of the 

 negative ion is the greater. It is also seen that for such 

 simple gases as and N the difference is considerable, while 

 for C0 2 there is no appreciable difference, a result which 

 could scarcely be anticipated. It would appear from these 

 results that some relation exists between the ion and the 

 charge carried by it which is dependent upon the sign of the 

 charge, and which varies with the constitution of the ion. 



In contemplating the cause of the difference of velocity of 



