SOME NUCLEI OF CLOUDY CONDENSATION. 25 



the air and gases over it, but obtained little indication of nuclei being formed. It 

 should, however, be kept in view that it is quite possible the sun may produce the 

 nuclei found at Kingairloch in some other way than from gaseous impurities in the 

 atmosphere, and the phenomenon will require to be further investigated at that place. 



These experiments on the effect of sunshine on the gases in the atmosphere show 

 that it is possible for cloudy condensation to take place in the absence of dust. That 

 is, supposing there is any part of the upper air free from dust, it is possible, if any of the 

 gases referred to be present, for the sun to convert them into nuclei of condensation, and 

 permit of clouds forming in dustless air. In the lower atmosphere there always seems 

 to be plenty of nuclei to form cloudy condensation whether the sun shines or not. The 

 only case where almost no nuclei were detected in the air was at the Ben Nevis 

 Observatory, where on one occasion, at least, Mr Rankin found the air nearly free from 

 dust, whilst the top of the mountain was in cloud. All the nuclei there at the time 

 seemed to have been used up to form fog particles, and the air was then in a peculiarly 

 supersaturated condition. 



Though it is here shown that the impurities in the atmosphere when acted on by 

 sunshine may permit of cloudy condensation taking place in the absence of what is 

 commonly known as dust, we are not yet in a position to say that they do act in this 

 way, because the impurities may not be in sufficient quantity to give a large enough 

 number of nuclei to produce the cloudy form of condensation ; there may be only nuclei 

 sufficient to produce the rainy form of condensation. 



