I 



Photoijniphlr IfcscatrheH and Portraiture 303 



all in the matter, and tlio HniailoHt amend that thoee who introduced him there can make, ia to 

 furnish him with tli<> iiiohI S4>rvio<Mil>l<- of all information to him, the complete iife-historie* 

 of all liis near progenitors." (p. 31.) 



The idea oi* portraiture as expressing mental character and that of indi- 

 viduality lis measured hy deviation from type fascinated Galton throughout 

 the whole of his long life, and he returned to these subjects with great energy 

 even in his last years. He sought to measure the degree of resemblance or 

 of dirt'erence in portraits. The amount of lalK)ur he put into this research 

 was immense; there is a great nuiss of manuscript matter, there are endless 

 profiles drawn by his jissistants, there are models of apparatus and there is 

 apparatus itself. Without a more detinite key than we possess it is ollen 

 very ditticult to trace what line of thought he was following up, although 

 not infrequently one lights on most suggestive ideas in side tracKs from tne 

 main problem. 



That the work in this direction arose from the composite photograph 

 investigations is clear from a lecture Galton gave on May 25, 1888 at tne 

 Royal Institution, entitled "Personal Identification and Description'". It 

 opens with the following words: 



"It i.s strange that wo should not have acquired more power of describing form and personal 

 features than we actually (wsse-ss. For my own part I have fre(|uently chafed under the .senile 

 of inability to vi-ibally e.^cplain hereflitary resemblances and type.s of feature.s, and to describe 

 irregular outlines of numy diff"erent kinds, which I will not now particularise. At last I tried 

 to relieve myself as far as might l)e from this embarrassment, and took considerable trouble, 

 and made some experiments. The net result is that while there appear to be many wa3-8 of 

 approximately effecting what is wanted, it is ditHcult as yet to stsleet the l)est ot them with 

 enough assurance to justify a plunge into a rather serious undertaking. According to the 

 Kivnch proverb, the Wtter has thus far proved an enemy to the pas.sably g<«xl, so I cannot go 

 uiucli into detail at present, but will chicHy dwell on general principles." {Xature, Vol. x.xxvni, 

 p. 173.) 



CJaltoii then states that while recognising different degi'ees of likenes.s 

 and unlikenesa we have not so far as he knows made any attempt to measure 

 theui. He now proposes to take for his unit of measurement the least-dis- 

 ceiiiihle difference. 



"The measui-ement of resemblance by units of least-discernible difference is applicable to 

 shades, colours, sounds, tastes, and to sense-indications generally." 



(ralton illustrates his method on sight differences; he takes two superpo.sed 

 oval contours (see Fig. «, Diagram iv, p. 304), intersecting one another, and 

 then halves the distance between their boundaries for a new contour, and 

 then halves again until he reaches — in his case in the fourth stage — a contour 

 indistinguisluil)le from one of the original contours. He then says there are 

 16 gi-ades of least-discernible difference between A and B. The method is 

 suggestive, but obviously liable to diftieulties, for it is clear that its measure- 

 ment is largely subjective. It de])ends on the fineness of drawing of the 

 original contours and of the subdividing contours. It depends also on the 

 scale upon which they are drawn. It is modified by the subjective conditions 

 of the observer, whether his sight is good, and whether he uses or does not 



' Nature,yo\.xx\vi\i, pp. 173-77, 201-2, 1888; Proc. Royal Institution, Vol. xii, pp. 346-60, 

 1889; my references are to the pages of Nature. 



