PJi(ttofiriii>hU' litM'drt'heH and Porfraifiire 305 



liertillon divides each of his four fiindamentnl characters into three groups 

 -large, nu'diuiii, small —and (Jiiltoii points out that the diflerenc*' hftwrcn the 

 men at the extremes of the medium group is, for stature, say 2;i inches while 

 I the possihle error of determining stature may Ije ± 05 inclj ; that is to say, 

 that there is a total doul)tful range of 2 inches, while the medium range 

 itself is oidy 2;3 inches. He further points out that nearly all Hertillon's 

 characters, we may anticipate, will he highly correlated together and accord- 

 ingly his 81 ( = 13*) groups will contain very unequal nuiiibers. 



"No iittfinpt lias yet been iiimie to CNtiniiite the dcgn-o of tliotr intordopeiidencf. I nm 

 thoreforc having the uliove ineasuroinonts (witli nli^ht nowsMjiry variations) recorded at my 

 anthropometric laboratory for the iiurjxise of doinjj so." (p. 175.) 



I do not think the.se measurements were ever taken in adequate numlxjrs 

 oi- that Galton ever determined actually their correlations. This was, I 

 believe, first done by the late Dr Macdonell, on actual criminal data, and he 

 j)ointed out lunv, by the use of proper "independent vari.itos " the trouble of 

 correlation in the characters could be eliminated'. 



The first difficulty, however, of the border-line cases, wliicli involve .such 

 a large proportion of the population and therefore the multiplication of 

 cards in several groups, Galton got over by what he termed a "mechanical 

 selector." I have not foimd any 'selector' described l)efore 1888, but many 

 since, all involving Galton's principle, some patented, without any recognition 

 of Galton's priority. The idea is inileed a very simple one; each individual 

 has a card 8 to i) inches long. If there are 4 or G indexing characters each 

 is allotted something less than a quarter to a sixth of the card. This 

 portion of the cjird represents the range of the corresponding variate and a 

 notch is cut into the curd at the value of the variate within this range". The 

 breadth of this notch represents twice the possible error of measurement, once 

 in excess and once in defect, for that variate. The cards are placed vertically 

 and loo.sely in a box divided into batches by partitions so that there is not 

 sufficient friction to interfere with their independent motion. The Iwttom of 

 the box, except sutlicient at the ends for the cards to rest on, is replaced by a 

 "keyboard" as Galton termed it; this keyboard is of the breadth of the 

 variate portion of the cards, and can be elevated by a lever. Adjustable wires 

 can l)e arninged across a gap in the keyboard of tiie size of the series of cards, 

 and these wires are adjusted to give the measurements of an individual to 

 be selected, just as the notches are cut in the cards. When the keyboard is 

 elevated its wires pjiss into the notches of those cards which are within 

 possible erroi-s of the individual set on the keyboard — all the other cards but 

 these are raised and thus discriminated from those which require examination. 

 It is clear that the cards do not require classification by size of organs, but 

 may be placed by age or alphabetically. Galton considered that this mechanical 



' Biome/rika, Vol. I, pp. 177-227. The Bertillon system of indexing by physical measure- 

 ments luus now Iwen replaced by direct indexing of finger-prints. 



- Actually the notch would nt)t be cut at the exact value of the variate except when neiir 

 the boundarj- of the sul)-rangc; in other positions it would suffice to cut it at the middle of the 

 sub-range. For Bertillon s index it would suttice practically to have pin points marked for each 

 variate on tlie card, where notches should bo cut. 



p o u 39 



