1879.] Mr, F, Gallon on Generic Images. IGl 



WEEKLY EVENING MEETING, 



Friday, April 25, 1879. 



The Duke of Northumberland, D.C.L. LL.D. the Lord Privy Seal, 

 President, in the Chair. 



Francis Galton, Esq. F.R.S. M.R.I. 

 Generic Images.* 



In the pre-scientific stage of every branch of knowledge, the pre- 

 valent notions of phenomena are founded upon general impressions ; 

 but when that stage is passed and the phenomena are measured and 

 numbered, many of those notions are found to be wrong, even absurdly 

 so. This is the case not only in professional matters, but in those 

 with which everyone has some opportunity of becoming acquainted. 

 Think of the nonsense spoken every day about the signs of coming 

 weather, in connection, for example, with the phases of the moon. 

 Think of the ideas about chance, held by those who are unacquainted 

 with the theory of probabilities; think of the notions on heredity, 

 before the days of Darwin. It is unnecessary to multiply instances ; 

 the frequent incorrectness of notions derived from general impressions 

 may be assumed, and the object of the following discourse is to point 

 out a principal cause of it. 



Attention will be called to a source of error that is inherent in our 

 minds, that vitiates the truth of all our general impressions, and which 

 we can never wholly eliminate except by separating the confused facts 

 upon which our general impressions are founded, and treating them 

 numerically by the regular methods of statistics. It is not sufficient 

 to learn that an opinion has been long established or held by many, 

 but we must collect a large number of instances to test that opinion, 

 and numerically compare the successes and the failures. 



Our general impressions are founded upon blended memories, 

 and these latter will be the chief topic of the present discourse. An 

 analogy will be pointed out between these and the blended portraits 



* This memoir is in part an abstract, and in small part ota extension of the 

 discourse that was actually delivered. The greater part of the subject matter has 

 been treated more fully in the July number of the ' Nineteenth Century,' but the 

 autotype illustrations which are given here are not inserted there. 



