IX. On the condensation nuclei produced in gases by the action of Röntgen rays. Uranium rays, ultra-violet light, and other agents

In a previous communication (‘Phil. Trans.,’ A, vol. 189, p. 265, 1897) I described experiments proving that when dust-free air, initially saturated with water vapour, is allowed to expand adiabatically, condensation takes place, if the maximum degree of supersaturation resulting from the expansion exceeds a certain limit. Using v2/v1 the ratio of the final to the initial volume as a measure of the expansion, we may describe the phenomena briefly as follows :— Condensation only takes place throughout the gas if v2/v1 exceeds 1.25; the drops are comparatively few, provided a second limit (v2/v1 = 1.38) is not exceeded. Beyond this second limit the rate of increase in the number of drops with increasing expansion is extremely rapid, very dense fogs resulting from expansions even slightly exceeding this limit.