HEREDITY 305 



The mathematician who most frequently helped 

 me later on was the Rev. H. W. Watson, who 

 moreover worked out for me the curious question of 

 the " Probability of the Extinction of Families " [40]. 

 It appeared in 1875 in the Proceedings of the Royal 

 Society as a joint paper, at his desire ; but all the hard 

 work was his : I only gave the first idea and the 

 data. He helped me greatly in my first struggles 

 with certain applications of the Gaussian Law, which, 

 for some reasons that I could never clearly perceive, 

 seemed for a long time to be comprehended with 

 difficulty by mathematicians, including himself. They 

 were unnecessarily alarmed lest the well-known rules 

 of Inverse Probability should be unconsciously violated, 

 which they never were. I could give a striking case 

 of this, but abstain because it would seem deprecia- 

 tory of a man whose mathematical powers and ability 

 were far in excess of my own. Still, he was quite 

 wrong. The primary objects of the Gaussian Law 

 of Error were exactly opposed, in one sense, to those 

 to which I applied them. They were to get rid of, 

 or to provide a just allowance for errors. But these 

 errors or deviations were the very things I wanted to 

 preserve and to know about. This was the reason 

 that one eminent living mathematician gave me. 



The patience of some of my mathematical friends 

 was tried in endeavouring to explain what I myself 

 saw very clearly as a geometrical problem, but could 

 not express in the analytical forms to which they were 

 accustomed, and which they persisted in misapplying. 

 It was a gain to me when I had at last won over Mr. 

 Watson, who put my views into a more suitable 

 shape. H. W. Watson was Second Wrangler of his 

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