﻿416 Mr. H. Pealing on Condensation Nuclei 



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day the effect diminished to a slightly tinted cloud. When 

 the glass-wool was dried again by drawing dust-free air 

 through it for a few hours, the effects obtained were again 

 largely increased. These effects were very persistent, and 

 experiments continued for more than a fortnight (during 

 which dust-free air was drawn through the glass-wool for 

 days) failed to remove the effect. By eliminating to a large 

 extent the iodine, the effects were reduced but not got rid of, 

 no doubt because of the difficulty of entirely getting rid of 

 the iodine by simply drawing air through. The presence 

 of fresh iodine quickly increased the effect again. The 

 effect did not disappear when dry dust-free air was used in 

 place of the ordinary air of the laboratory. After the glass- 

 wool plug had been treated in this manner, it was left 

 standing for a fortnight. The effect was found to have 

 almost disappeared, but it reappeared when a few cubic centi- 

 metres of distilled water was drawn through, but the effect 

 this time was not so persistent and disappeared almost 

 entirely in the course of a few days. A similar amount of 

 fresh distilled water brought back the effect, and this time 

 it was very persistent. These experiments were made in 

 Cape Town. Through the kindness of Professor Wilberforce 

 T was able to repeat some of them at Liverpool University, 

 using another apparatus and a different kind of glass-wool. 

 The glass was obtained in the spun condition and was cut 

 into lengths and the fibres separated just previous to the 

 making of the plug used in the experiments, the result being 

 somewhat heterogeneous glass-wool. A more important 

 variation from the Cape Town experiments was in the water 

 used to renew the effect in the glass-wool. This was of 

 special purity, and was supplied to me through the courtesy 

 of Mr. Powell of Liverpool University. The water was of 

 the degree of purity required for accurate determinations 

 of the resistivity of solutions. In this case also the effect 

 was renewed in the glass-wool when a few cubic centimetres 

 of this specially purified water was drawn through the plug. 



Discussion of Results. 



These experiments show that the purest water obtainable 

 renews the effect in any kind of glass-wool. The conclusion 

 drawn is that the effect does not depend in any way on the 

 impurities which water contains. Other reasons supporting 

 this conclusion are given further on. The fact that the effect 

 can be renewed seems to prove that the effect is not caused 

 by any impurity on the glass-wool. Owen and Pealing have 

 shown that the effect obtained by the interaction of the 



