186 



Life and Letters of Francis Galton 



Here again we have to remember that the amount of resemblance is not 

 really measured by the numbers given ; they might, as in the previous case, 

 be merely the result of chance. Let us work out how much is due to chance 

 in the case of the thumb and ring finger. 



Percentage of Cases in which the same Class of Pattern occurs 

 in Thumb and Ring Finger. 



The numbers remain very close, when we have deducted the resemblances 

 due to chance, but perhaps do not look so impressive. Only about one-sixth 

 of the resemblances in both cases can be attributed to the organic relationship. 



Galton, on pp. 122-129, discusses a somewhat unusual method of deter- 

 mining the degree of association between the patterns on any two digits. 

 To illustrate it let us take loops on the ring fingers of left and right hands. 

 These occur in 66 / o and 53°/ o of cases. Or, the chance of a loop is — if the 

 results were independent — 100 x T %^ x ^^ = 35% nearly. The maximum 

 possible number of loops common to the two fingers is 53% and the actually 

 observed number is 46°/ c . We have then the three numbers 35, 46 and 53. 

 Galton takes the first as a zero relationship and the last as a perfect 

 relationship, which is represented by him as 100°. On the scale in which 35 



represents 0° and 53, 100°, we must have 46 = 



48-35 

 53-3S 



100° = 4^ 100° = 61° 



He gives a table for these grades of association on p. 129 between digits of 

 the same and of different hands. According to this table the highest relation- 

 ship is between whorls on the middle and ring fingers (74°) and the lowest 

 between loops on fore and ring fingers (13°). Galton is himself somewhat 

 doubtful as to this method of measuring association, and I have not 

 accordingly reproduced his full table (p. 129). 



In Chapter IX (pp. 131-146) Galton deals with Methods of Indexing. 

 It does not carry us far beyond the Royal Society Proceedings paper (see 

 our pp. 170-174). In his main method Galton breaks up only the loops on 

 the forefingers into "inner" and "outer."* He represents these by i and o. 

 Thus five symbols are used : a = arch, I = loop, w = whorl, and i = inner loop on 

 forefinger, o = outer loop on forefinger. He breaks his ten-letter index into 

 four groupsf , i.e. K hand, fore, middle and ring fingers; L. hand, fore, middle 



* The reader must remember that the finger-print is reversed, and not be surprised at Galton 

 labelling "inner" what appears to the reader, looking at his hand, as an "outer" slope. 



f The reason for this has already been referred to (see our p. 184), namely, the greater variety 

 in the types of forefinger prints. 



