304 Lift ami Letters of Francis Galton 



use glasses. Also it is clear that the least-discernible difference may he 

 reached at some points long before it is reached at others, or the measure 

 of resemblance would vary from part to part, and ultimately be a measurt- 



d 



Fig. n. Fig. i. Fig. e. 



Diagram iv. 



of only the most unlike parts. If we agree to an average fineness of line, and 

 an average keenness of sight, we shall still be left with the question of scale'. 

 Dealing with the silhouette, Cralton remarks that: 



"All human profiles of this kind, when they have been re<luct>d to a uniform vertical scale, 

 fall within a Hniall space. I liavf- taken those given by I^avater, which are in many cases of 

 extreme shapes, and have added others of Hnf^iish faces, und tliey all fall within the space 

 shown in Fig. Ij. [Galton is working with the distance from the notch that separates the brow 

 from the nose (nasion) to the parting of the lips as standard length.] The outer and inner 

 limits of the sj>ace are of course not the profiles of any real faces, but the limits to many 

 profiles, some of which are exceptional at one point and others at another. We can classify 

 the great majority of profiles st) that each of them shall be included lietween the double borders 

 of one, two, or some small numlier of standard portraits, such as Fig. c. T am as yet unpre- 

 pared to say how near together the double l)orders of such standard portraits .should l>o <lrawn : 

 in other woi-ds, wlmt is the smullest numl>er of grades of unlikeness that we can satisfactorilv 

 deal with. The process of sorting profiles into their pro|>er classes, and of gradually building up 

 a well-selected .standard collection, is a lalxtrious undertaking if attempted in any obvious way, 

 but I believe it can lx> effet'ted with comparative ea.se on the i>asis of measurements as will b<' 

 explained later on, and by an apparatus that will lie descrilnxl." (p. 174.) 



The reader will now be able to perceive better what Galton was really 

 attempting to do by this special illustration: he was aiming at identifying 

 individuals by their profiles, and in order to do this it was needful to index 

 profiles. Tiiis leads Galton to the topics of indexing and of entering indices. 

 He first refers to Bertillon's system of identifying criminals, and states that 

 tiie actual method by which it is done is not all that theoretically could be 

 desiretl. He notes a fundamental difficulty that arises : 



"The fault of all hard-and-fast lines of classification when variability is continuous, is the 

 donbt where to place and where to look for values that are near the limits between two adjacent 

 clasMB." (p. 175.) 



' For example, siijijmwc a be required to find the degree of resemblance between t»ii umjis, 

 A and /i, of the same district on different scale*; shall we reduce A to R, or H Xio A, for that 

 will clearly affect our judgment? Or, shall we look at them both placed on the table before 

 us, or both hung at some little distance on a wall? 



