I luster in a Gas wider Influence of an Electric Field. 921 



obtained with carbon dioxide at a pressure of: 4 mm. of mercury 



with the negative ions, and the curve B that obtained with the 



positive ions. The distance I between gauze and plate was 



1 cm. The curve G was obtained on plotting the logarithms 



(multiplied by 10 for convenience) to the base 10 of the 



currents obtained with the negative ions against the electric 



field. On plotting the logarithms (multiplied by 10) of the 



currents that would be obtained if the total number of ions 



drawn through the gauze were independent of the field when 



it is large and no clusters became free ions, we obtain the 



curve D. Tins amounts to plotting the values of 10 log 10 n e Ia 



10 

 or (log n + la) -^ for different values of a, where n , the 



number of free ions drawn through the gauze, is obtained 

 from the equation log w + Za = 2-31og l0 O 1 , @i being the 

 current corresponding to the first point in the curve C, and 

 I the distance between gauze and plate. The values of a, the 

 collision coefficient for the negative ions, were obtained from 



the curves connecting — and - given by Townsend, where 

 6 p p 6 J 



X denotes the electric field in volts per cm. and p the pressure 



of the gas in mm. of mercury. The figure also shows curves 



obtained with air at a pressure of 3 mm. of mercury. It 



will be seen that the slope of the curve D is greater than 



that of the curve C in both cases. This indicates, we have 



seen, that the electric field over the region examined does not 



help to disintegrate an ion cluster; further, that a cluster is 



gradually disintegrated by being bombarded by neutral 



molecules. It will also be readily understood from what has 



gone before that if the disintegration of the clusters is 



principally due to the effect of the electric field, the curve D 



would lie below the curve C. A point should therefore exist 



at which the curve D cuts the curve C. This point is 



indicated by the trend of the curves in the figure. The 



number of clusters becoming free ions between gauze and 



]>late at this point is equal to the number becoming free at 



the starting point of plotting the curves. Since the number 



of clusters disintegrated between gauze and plate through 



bombardment by neutral molecules decreases with increase of 



electric field, the field at the point in question assists to a 



certain extent in the disintegration of the clusters. The 



observations from which the curves A, B, and C in fig. 2 



have been plotted are given in Table I. The letter L indicates 



when the current was so large that it could not be measured 



by the present form of the apparatus. 



