CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



suddenly in case of the new results, and it is perhaps higher than in the 

 old. No progress above the green corona could be obtained, but on the 

 other hand there was no decrement of nucleation at very high exhaus- 

 tions, such as is often obtained. 



57. Condensation limits and fog limits. Conclusion. The conden- 

 sation limits, or the exhaustions at which condensation begins, are best 

 gathered from fig. 29, which also shows the nearly constant low nuclea- 

 tion (due, as C. T. R. Wilson has proved, to ions), which precedes the 

 region of vapor nuclei in the case of dust-free wet air. 



D is the distance from which the X-ray tube acts. 



It appears certain from these results that the condensation limit 

 decreases slowly as the intensity of radiation increases; also that it is 

 lower for ionized air, even under weak radiation, than for dust-free 

 normal air. Coronas may be obtained in succession, in these instances, 

 after they have completely vanished in the preceding case of weaker 

 radiation. Rain is naturally accompanied by a definite corona. If we 

 reckon the intensity of the radiation as the square of the maximum 

 radiation producible, or the height of the asymptote, the following data 

 may be adduced from figs. 28 and 29: 



Thus, while the intensity of radiation changes from the natural radia- 

 tion in dust-free air, i, to io 4 for beta-gamma radiations, and from i to 

 io 6 for X-rays, the volume expansion at which condensation takes place 

 shifts over decrements of 0.015 and 0.020 or 15/1240 and 20/1240, 

 i. e., 1.2 per cent and i . 6 per cent. 



