918 Dr. R. D. Kleeman on Disintegration of an Ion 



unaltered by the field. The cluster will then pass over a 

 distance / at the end o£ which it will have become dis- 

 integrated owing to bombardment by the neutral molecules. 

 If the intensity o£ the electric field is doubled and it still 

 does not affect the process of disintegration of the ion cluster, 

 the distance it traverses before disintegration is 21, or, 

 generally, under these circumstances the distance traversed 

 is proportional to the intensity of the electric field. But on 

 increasing the electric field sufficiently, a point will be 

 reached when it affects the disintegration of the ion cluster, 

 the distance it traverses being then less than proportional to 

 the electric field. It will be observed that an increase in the 

 electric field at this point still produces an increase in the 

 distance traversed by the ion cluster. On further increasing 

 the electric field, however, a point will be reached when an 

 increase in electric field produces a decrease in the distance 

 traversed by the cluster. The distance then continually 

 decreases with further increase of the electric field. The 

 distance the ion cluster traverses from the instant of its 

 formation to that of its disintegration may be called its free 

 path of disintegration corresponding to the electric field 

 applied. The free path thus passes through a maximum as 

 the electric field is gradually increased. This path is probably 

 not always the same under constant conditions, since the 

 history of the collisions of the cluster with neutral molecules 

 is not always the same, being subject to probability. But 

 there should exist a mean free path about which the different 

 paths are grouped in a similar way as the different paths of a 

 molecule in a gas about its mean free path. 



Similar considerations should apply to the free or elementary 

 ions in a gas. Thus there should exist a mean free path of 

 formation of a cluster corresponding to the field applied 

 which depends on the nature of the cluster. This mean free 

 path would be proportional to the field applied over a certain 

 range beginning from zero upwards, while for more intense 

 fields it would be greater. A limiting value of the field 

 would thus exist for which the free ion never forms a cluster, 

 or the mean path is infinite. Ionization by collision probably 

 begins to come in for a field smaller than this limiting 

 value. 



The behaviour of ion clusters under the action of an 

 electric field was studied by drawing ions produced in a 

 comparatively weak field through a gauze into a much 

 stronger field, and measuring the current for electric fields of 

 different strengths, including fields sufficiently strong to 



