290 



Miss M. Beeton and Prof. Karl Pearson. 



tive ions is, say, twice as great as that carried by the positive ions, for 

 equal numbers of positive and negative ions are produced by the 

 ionisation of the neutral gas. 



Attempts were now made to find an answer to the first question 

 suggested above — Is there any evidence that ions are likely to be 

 present under normal conditions in the atmosphere 1 



Former experiments furnished a certain amount of evidence in 

 favour of an affirmative answer. 



When moist dust-free air is allowed to expand suddenly a rain-like 

 condensation always take place if the maximum supersaturation exceeds 

 a certain limit. This limit is identical with that required to make 

 water condense on ions ; the identity is in fact so exact as to furnish 

 what is at first sight almost convincing evidence that ordinary moist 

 air is always to a very slight extent ionised. The number of these 

 nuclei is too small to make the absence of sensible electrical con- 

 ductivity in air under ordinary conditions inconsistent with the view 

 that they are ions. 



All attempts, however, to remove these nuclei, by applying a strong 

 electric field such as would have removed ordinary ions almost as fast 

 as they were produced, have failed, even when a differential apparatus 

 was used, such as would have made manifest even a slight diminution 

 in the number of the nuclei by the action of the field. The same is 

 true of the similar nuclei produced by the action of weak ultra-violet 

 light on moist air. 



Such nuclei, therefore, in spite of their identity as condensation 

 nuclei with the ions, cannot be regarded as free ions, unless we suppose 

 the ionisation to be developed by the process of producing the super- 

 saturation. This question requires further investigation. 



" Data for the Problem of Evolution in Man. II. A First Study 

 of the Inheritance of Longevity and the Selective Death-rate 

 in Man." By Miss Mary Beeton and Karl Pearson, F.Pt.S., 

 University College, London. Keceivecl May 29, — Read June 

 15, 1899. 



1. According to Wallace and Weismann* the duration of life in any 

 organism is determined by natural selection. An organism lives so long 

 as it is advantageous, not to itself, but to its species, that it should live. 

 But it would be impossible for natural selection to determine the fit 

 duration of life, as it would be impossible for it to fix any other 

 character, unless that character were inherited. Accordingly the 

 hypothesis above referred to supposes that duration of life is an 



* See Weismann, ' On Heredity,' Essays I and II, and especially Professor 

 Foulton's note as to Wallace, p. 23, of first English edition. 



