Cluster in a Gas under Influence of an Electric Field. 937 



clusters that can exist in a gas.. It appears from a study of 



the curves that the clusters consist largely, if not exclusively, 



of clusters of one kind. Of course some of the clusters, 



especially complex ones, might get broken up through the 



action of the electric field before ionization by collision comes 



in. The kinks would be absent in this region. The number 



of such clusters, if they exist, is, however, much smaller than 



the number corresponding to the one kind of cluster which 



is conspicuously stable. Thus consider the curve C in fig. 3 



for C0 2 . It shows one kink only, evidently of the second 



order. The calculated number of free ions drawn through 



the gauze that would account for the current corresponding 



to the point b is about '02 per cent, of the total number of 



ions drawn through the gauze. The calculated number of 



free ions corresponding to the point d we have seen is 



practically equal to the number of ions drawn through the 



gauze. Thus practically all the clusters become elementary 



ions over the region od, and consist of one kind only since 



the part of the curve C for this region shows one kink only. 



The curve C for H 2 in fig. 7 also shows one kink only which 



is of the second order. The apparent percentages of the 



numbers of ions drawn through the gauze which are in the 



form of clusters corresponding to the fields 800 and 1120 



volts per cm. are roughly 95 and 38 respectively. Thus 



about 60 per cent, of the clusters become free ions over the 



region ob, and consist at least approximately of clusters of 



one kind. With air at a pressure 2*5 mm. of mercury there 



appears no kink in the region od of the curve C in fig. 6. 



But w T hen the pressure is 3 mm. of mercury a kink appears, 



as shown by the curve E in the figure. At a pressure of 



6 mm., however, again no kink appears. We shall see 



presently that the position of the kink on the logarithm 



current curve for any given cluster varies in a complicated 



way with the pressure of the gas and the strength of the 



electric field. 



The kinks in the curve, we have seen, indicate when the 



mean free path of a cluster is equal to the distance between 



gauze and plate. Thus the mean free path of a cluster in 



00 2 at a pressure of 4 mm. of mercury is equal to *5 cm. 

 •y 



when the value of — is equal to 930. At a pressure of 

 p 



2*3 mm. of mercury the mean free path is equal to the same 



X T X 



distance when - has the value 348. When has the 



P P 



value 64 in hydrogen at a pressure ot 15 mm. of mercury, the 

 mean free path is also equal to *5 cm. The disintegration of 



