GENERIC IMAGES. 533 



that were derived from general impressions are discovered to be wrong, 

 even absurdly so. I do not speak only of such matters as astrology 

 and alchemy, but of those also with which most persons are acquainted. 

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

 in connection, for example, with the phases of the moon, and firmly 

 believed in by many respectable people. Think of the ideas about 

 chance, held by those who are unacquainted with the theory of proba- 

 bilities. Think of the notions entertained on heredity before the days 

 of Darwin. Think of the ridiculous nostrums that have been pre- 

 scribed for common ailments by gifted and experienced practitioners, 

 the merits of which have been also vaunted by the invalids who tried 

 them. # It is not necessary to go into more detail in illustration of the 

 fallacies of popular generalizations. The list of them is endless ; they 

 are to be abundantly found, as already observed, in every branch of 

 knowledge, before it has been seized in the firm and sure grasp of pro- 

 cesses that depend upon exact measurement and number. That popular 

 notions are habitually incorrect may be taken for granted, and my pur- 

 pose in this memoir is to explain one cause of their incorrectness. 



I propose to call attention to an error in the operations of the mind, 

 whenever it blends memories together, and to show why the brain is a 

 faulty apparatus for elaborating general impressions. I shall argue 

 that we have no means of correcting its necessarily fallacious results, 

 except by picking them to pieces, and going back to the facts whence 

 the general impressions were derived, and by dealing with those facts 

 on true statistical principles. Thus if we hear that some medical nos- 

 trum is highly reputed, or that some particular appearance is an excel- 

 lent prognostic of coming weather, our first step toward investigating 

 the truth is not to ask whether the belief is firmly held, or of old 

 standing, or shared by many, but to obtain a considerable number of 

 instances and to set off the failures against the successes. 



The general impressions and ideas to which I refer guide the great 

 majority of our every-day actions. We have a general impression that 

 the day looks rainy, and we take an umbrella. We find ourselves in a 

 railway-carriage with a person who looks sociably inclined and agree- 

 able, and we accost him accordingly. 



In an infinity of cases like these, the opinion on which we act has 

 not been formed by any process of reasoning ; neither has it been made 

 by considering what similar experiences we have had, and counting 

 their results on this side and on that, but it is the effect of blending 

 together a large number of similar incidents. These blended memories 

 are the subject of my present memoir. I shall try to prove that blended 

 memories are strictly analogous to blended pictures, of which I have 

 produced many specimens by combining actual portraits together ; and 

 I shall explain the peculiarities of the images by those of the portraits ; 

 then I shall show that the brain is incompetent to blend images in their 

 right proportions. My conclusion will be that our unreasoned impres- 



