REGIONS OF MAXIMUM IONIZATION. 47 



37. Inferences. At first sight one would conclude that in a region of 

 maximum ionization there must either be a larger rate of production or 

 a smaller coefficient of decay. The latter might be expected if in the 

 given region the ions had largely the same sign. The frequent occurrence 

 of the ionization ratio 2 to i in the earlier work lent some plausibility 

 to this view, but the later experiments with a much longer fog chamber, 

 and where much greater ratios occur in the ionizations of different parts of 

 the chamber, quite disprove this surmise. The correlative view that the 

 maximum might be referred to the superposition of primary and second- 

 ary radiations from different parts of the fog chamber is negatived by 

 changing the character of these parts from glass to metal, or the reverse. 

 Hence the maximum of ionization obtained must be associated with the 

 exhaustion itself for in each case the displacement of the maximum 

 is from the radium, wherever placed, to the exhaustion end of the fog 

 chamber. And, in fact, since the exhaustion amounts to a volume ratio, 

 v l /v, if vapor pressures be neglected, and 



v 1 _P'( 1 ~ clk )p clk +[v/V]p 



where p f 46 cm. at the vacuum chamber, p=j6 cm. at the fog chamber, 

 Pa = 5 1 cm., the final common isothermal pressure when both chambers 

 are in communication, and where the volume ratio of the chambers [v/F] 

 = 0.3 nearly, the exhaustion is about V I JV=I.T ) T > . Hence the bodily 

 displacement of air at the exhaust end would be 36 cm., and at the middle 

 1 8 cm. if the fog chamber were cylindrical. The conical form with the 

 small end at the exhaust pipe would considerably enhance this bodily 

 transfer of air from the closed to the exhaustion end of the chamber. 

 Thus we infer, if the radium is at the closed end, that is, at the extreme 

 distance from the exhaustion end, the maximum should lie there also, 

 since there is no appreciable displacement of air. In proportion as the 

 radium lies nearer the exhaustion end of the fog chamber, the displace- 

 ment of maxima of ionization will be greater, compatibly with the greater 

 bodily displacement of air, until in the case of the conical chamber, no 

 cm. long, like the above, the displacement may exceed 40 cm. Further- 

 more, at the exhaustion end there will never be a proportionately large 

 maximum, because the ionization has been removed into the vacuum 

 chamber, and the whole series of coronas is of exceptionally small size 

 throughout, due to increasing distance from the radium. In fact, it can 

 hardly be said that any specific evidence of the occurrence of an appre- 

 ciable secondary radiation has been adduced by the experiments. 



In this way the above phenomena are at least qualitatively accounted 

 for, as it must be acknowledged the displacement is often larger than the 

 data here estimated, the reason for which is not sharply determinable 



