166 Mr. Francis Gallon [April 25, 



a matter of observation, the resemblance between persons of the same 

 " genus " (in the sense of " generic," as already explained) is suffi- 

 ciently great to admit of making good pictorial composites out of 

 even small groups, as has been abundantly shown. 



Composite pictures are, however, much more than averages ; they 

 are rather the equivalents of those large statistical tables whose totals, 

 divided by the number of cases, and entered in the bottom line, are 

 the averages. They are real generalizations, because they include 

 the whole of the material under consideration. The blur of their 

 outlines, which is never great in truly generic composites, except 

 in unimportant details, measures the tendency of individuals to 

 deviate from the central type. My argument is, that the generic 

 images that arise before the mind's eye, and the general impressions 

 which are faint and faulty editions of them, are the analogues of 

 these composite pictures which we have the advantage of examining 

 at leisure, and whose peculiarities and character we can investigate, 

 and from which we may draw conclusions that shall throw much light 

 on the nature of certain mental processes which are too mobile and 

 evanescent to be directly dealt with. 



A generic mental image may be considered to be nothing more 

 than a generic portrait stamped on the brain by the successive impres- 

 sions made by its component images. Professor Huxley, from whom, 

 as already mentioned, the apt phrase of " generic " has been borrowed, 

 has expressed himself to a similar eifect in his recent life of Hume 

 (p. 95). I am rejoiced to find that, from a strictly physiological side, 

 this explanation is considered to be the true one by so high an 

 authority, and that he has, quite independently of myself, adopted a 

 view which I also entertained, and had hinted at in my first description 

 of composite portraiture, though there was not occasion at that time 

 to write more explicitly about it. 



In my original memoir on composite portraits a phrase was used 

 which was written with some hesitation, and which I have since quoted, 

 but which it will now be the object to examine and amend. The 

 words were : " A comi^osite portrait represents the picture that would 

 rise before the mind's eye of an individual who had the gift of pictorial 

 imagination in an exalted degree." The question to be considered is 

 whether this is a strictly correct statement. If the eye of such a man 

 were placed in the position of the object-glass of a camera when 

 taking the composite portraits, and if we supj)ose him free from 

 mental bias, would the resulting picture in his brain be identical with 

 the composite ? (Here again we are suj^posed to ignore such small 

 difierences as may exist between the photographic and optical compo- 

 site.) The answer is distinctly. No. Suppose that one of the portraits 

 has been exposed for a period fifty times as long as any of the rest, in 

 the photographic composite the effect would be the same as that of 

 fifty coats of transj^arent pigment, but in the mental composite 

 it would have nothing like that importance; and therein lies the 

 source of error in our mental impressions that it is the object of 



