Mr Kleeman, The Unstable Nature of the Ion in a Gas. 271 
1360 volts percm. From the curve for CO, giving* the relation 
between = and = we obtain : = 1:62 corresponding to 
X 1360 
ESSA 140, 
and hence a=15°39. Let n, denote the initial ionisation that 
would account for this current. Then we have 187 = n,e°*%9, 
and hence n, = 064. The actual number of ions drawn through 
the gauze corresponding to a field of 1360 volts can most ac- 
curately be obtained by reversing the field and measuring the 
positive leak obtained. This leak was found to be equal to 25. 
Thus about -2 7% only of the ions drawn through the gauze need 
be in the elementary state to account for the current obtained. 
Actually a smaller fraction is in the free state since some of the 
clusters become elementary ions during their passage from gauze 
to plate, and augment the current due to collision of ions. The 
result obtained fits in with experiments described in a previous 
part of the paper, where it was shown that the position of the 
collision curve (fig. 2) with respect to the axes is greatly in- 
fluenced by radium brought near the chamber, though the initial 
ionisation was not increased by an appreciable degree. 
In the case of air (dried by bubbling it through strong H,SQO,) 
at a pressure of 15 mm. of mercury a current of 172 was obtained 
corresponding to a field of 1440 volts per cm. Now ae 
corresponding to ze = 96, and hence a=12°75. The value calcu- 
lated for n is thus 37. The total current through the gauze 
corresponding to 1440 volts per cm. was equal to 20. Thus less 
than 2°/ of the ions drawn through the gauze were in the free 
state. Ina similar way it was shown that a small fraction only 
of the negative ions drawn through the gauze when H, was in the 
chamber are in the free state. 
It might be suggested that the meshes of the gauze in causing 
the electric field to be non-uniform in its immediate neighbour- 
hood give rise to the results obtained. Thus the effective distance 
between gauze and plate may be smaller or greater than that 
which actually exists. If however the distance between the plate 
and an imaginary plane corresponding to the collision current for 
a constant voltage per cm. is calculated, it is found to be only 
14 of the actual distance between gauze and plate. It is quite 
certain from this number that the effect is not due to the meshes 
of the gauze. 
* The Theory of Ionisation by Collision, pp. 19—21. By Prof. J. S. Townsend. 
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