| Description | Volume A3 is again a record of data of laboratory experiments, following straight on after volume A2. Detailed results of work between 7 August 1896 and 30 November 1896, on critical supersaturation measurements in hydrogen, chlorine and nitrogen under the influence of X-rays are recorded. The next data of importance are those given under a heading 'difference between the efficiencies of positive and negative ions as condensation nuclei', dated 7 January 1899. Subsequent pages cover the period 7 January-2 March 1899, and show development of apparatus and results upon this subject, with the following important summary:
'General results of all the experiments. Negative ions begin to be caught about V[subscript2]/V[subscript1]=1.25 and all appear to be caught when V[subscript2]/V[subscript1]=1.28. Density of negative fog shows no increase from this point onwards. Positive ions begin to be visible about V[subscript2]/V[subscript1]=1.31. Fogs are constant and identical with the negative from 1.35 upwards.'
The record then continues (26 January 1900) with experiments utilizing radioactive sources and this appears to be the first systematic attempt to correlate condensation with ionization produced by such agencies, although (cf volume A6) some small reference is made to the use of uranium in February 1898.
Scattered through this and the earlier volumes there is occasional reference to experiments upon the influence of ultra-violet light and of metals in promoting condensation, and it is clear that these phenomena provided a recurrent theme of worry to Wilson. It is amusing to not that on the closing date of this volume (22 February 1900), after all of the brilliant experimental work and conclusions which had gone before, Wilson returns to this topic describing an experiment made 'with the object of seeing if nuclei due to presence of zinc were removed by strong field in presence of ions due to Roentgen rays'. |