﻿850 Dr. Carl Ramsalier on the Production of Condensation 



Our experiments were concerned with the action of ultra- 

 violet light of very short wave-length on gases, more espe- 

 cially air. By means of systematic precautions in the 

 drying and purifying of the gases, directed especially 

 against very small impurities which, although not otherwise 

 detectable, have here a very important influence, we suc- 

 ceeded in separating the different actions of the light 

 (chemical action, formation of nuclei, formation of electrical 

 carriers), and explaining the nature of effects due to their 

 coexistence, which are often very complicated. The quanti- 

 tative measurements were first made on the carriers of electric 

 charge, whose size and other particulars were obtained from 

 their velocity of wandering, determined by the cylinder 

 condenser method. The carriers thus measured arise from 

 the combination of larger nuclei, originally uncharged, with 

 carriers of molecular size, so these measurements give in- 

 formation concerning the size, number, and formation of the 

 nuclei themselves. The electrical measurements therefore 

 solve the same questions as can be answered by means cf 

 Wilson's experiment, as in the work of Mr. Owen *. 



It is thus possible for us to compare the results we 

 obtained with cooling directly with those of Mr. Owen f. 

 We observed the same facts as he did. If carefully dried air 

 is cooled to a low temperature, uncharged nuclei are formed, 

 which in our experiments, where the cooling was only used 

 for purification, were removed by passage through a filter, 

 also cooled. These nuclei, however, do not consist of 

 aggregates of air molecules, but of condensed gases (C0 2 , 

 NH 3 , organic vapours, last traces of H 2 0) present in small 

 quantities in the air, as follows from the fact that the 

 formation of nuclei by means of ultra-violet light observed 

 before no longer takes place after cooling. This formation 

 of nuclei is, however, immediately restored if the air, after 

 purification as above, passes over surfaces of any material, 

 though these may be clean in the ordinary sense (for instance, 

 a short, clean, glass tube which has not previously been 

 glowed). This is due to the surfaces spontaneously giving 

 off traces of vapour, which they have absorbed from the 

 atmospheric air. Only by heating all the walls of the vessel 

 to a dull redness, until the glass becomes soft, for instance, 



* Prof. Becker has worked out in this way an electrical method of 

 measuring the size of nuclei, by using- Hbnt'gen rays to produce the 

 carriers of electric charge, and so avoiding the complication of formation 

 of nuclei by the light itself. 



t Lenard and Ramsauer, loc. cit. See especially Tart III. 



