Mathematical Contributions to the Theory of Evolution. 241 



here obtained. The value obtained by E. Eutherford"^ for the velocity 

 of the negative ions produced in dry carbonic acid (0*78 cm. per second) 

 by the action of ultra-violet light, is quite near to that here obtained 

 (0'81 cm. per second) for the ions produced by Eontgen rays, but his 

 values for dry air (1-4 cm. per second) and dry hydrogen (3'9 cm. per 

 second) are considerably smaller. 



In discharge from points, A. P. Chattockf has obtained for the 

 velocities of the positive and negative ions in dry air 413 and 540 cm. 

 per second respectively for a field of 1 E.S.U. per cm., which values are 

 quite close to those obtained here for the ions produced by Eontgen 

 rays. 



J. S. TownsendJ has shown that from the coefficients of diflusion 

 of the ions and from their velocities it is possible to compare the 

 charges carried by the different ions, and also to compare them with 

 those carried by the ions in the electrolysis of liquids. By using the 

 velocities given above with the coefficients of diffusion determined by 

 J. S. Townsend, the values of Ne are obtained, N being the number of 

 molecules in 1 c.c. of the gas and e the charge carried by each ion. 

 The results thus obtained for the moist gases, air, oxygen, and 

 hydrogen, perhaps justify the statement that the charges carried by 

 the positive and the negative ions are equal, and that the charge is the 

 same for the different gases, and is equal to the charge carried by the 

 hydrogen ion in the electrolysis of liquids. 



The values of Ne obtained for the positive ions in these gases when 

 dry are considerably larger than the above, while in carbonic acid all 

 of the results are over 20 per cent, smaller. 



" Mathematical Contributions to the Theory of Evolution. VIII. 

 On the Correlation of Characters not Quantitatively Mea- 

 surable." By Karl Peaeson, F.E.S. Eeceived February 7, 

 — Eead March 1, 1900. 



(From the Department of Applied Mathematics, University College, London.) 



(Abstract.) 



1. In August last I presented to the Society a memoir on the inheri- 

 tance of coat-colour in thoroughbred horses, and of eye-colour in man. 

 This memoir, which was read in November of last year, presented the 

 novel feature of determining correlation between characters which were 

 not capable a iwiori of being quantitatively measured. The theoretical 



* E. Rutherford, ' Camb. Phil. Soc. Proc.,' vol. 9, Part YIII. 

 t A. P. Chattock, ' Phil. Mag.,' November, 1899. 

 X J. S. Townsend, 'Phil. Trans.,' A, vol. 193, 1899. 



