304 MEMORIES OF MY LIFE 



same mechanical problem had been solved still more 

 comprehensively by a French mathematician. Pro- 

 fessor Karl Pearson subsequently extended its ap- 

 plication to variables not governed by the Gaussian 

 Law, and the exact determination of the Index of 

 Correlation by his refined method has now become 

 the object of most biometric work. 



I have received much help at various times 

 from Mathematical friends. On one occasion, being 

 impressed with the probability (owing to Weber's 

 and Fechner's Laws) that the true mean value of 

 many of the qualities with which I dealt would be 

 the Geometric and not the Arithmetic Mean, I asked 

 Mr. Donald Macalister, of whom I have already spoken, 

 to work out the results. He, as a schoolboy, was the 

 first to gain the prize medal of the Royal Geographical 

 Society, then became the Senior Wrangler of his year 

 at Cambridge, subsequently Chairman of the Medical 

 Council, and is now Provost of Glasgow University. 

 His memoir is supplementary to mine on the 

 " Geometric Mean," Proceedings of the Royal Society, 



1879 [53]. 



My first serious interest in the Gaussian Law of 



Error was due to the inspiration of William Spottis- 

 woode, who had used it long ago in a Geographical 

 memoir for discussing the probability of the elevations 

 of certain mountain chains being due to a common 

 cause. He explained to me the far-reaching applica- 

 tion of that extraordinarily beautiful law, which I 

 fully apprehended. I had also the pleasure of making 

 the acquaintance of Quetelet, who was the first to 

 apply it to human measurements, in its elementary 

 binomial form, which I used in my Hereditary Genius. 



