350 -^*'» Francis Gallon [May 25, 



Then the ratio borne by the uncertain entries to the whole number of 

 entries is as c^ c. + e^ e.^ to A B. This, as seen by the diagram, is a 

 very large proportion. There is a dilemma from which those who 

 adopt hard-and-fast lines of classification cannot escape : either the 

 fringe of uncertainty must be dangerously wide, or else the delicacy 

 with which measures are made cannot be turned to anything like its 

 full account. If the delicacy is small, the fringe of uncertainty must 

 be very wide ; if the delicacy is great, the summed widths of all the 

 fringes will be narrow, so long as there are only a few classes ; but, 

 on the other hand, by having only a few classes, most of the advantages 

 of possessing delicate observations are wasted. The bodily measure- 

 ments are so dependent on one another that we cannot afford to 

 neglect small distinctions in an attempt to make an effective classi- 

 fication. Thus long feet and long middle-fingers usually go together. 

 We therefore want to know whether the long feet in some particular 

 person are accompanied by very long, or moderately long, or barely 

 lonf fino-ers, though the fingers may in all three cases have been treated 

 as lonf' in M. Bertillon's system of classes, because they would be 

 long as compared with those of the general population. Certainly his 

 eic'hty-one combinations are far from being equally probable. The 

 more numerous the measures the greater would be their interdepend- 

 ence and the more unequal would be the distribution of cases among 

 the various possible combinations of large, small, and medium values. 

 No attempt has yet been made to estimate the degree of their inter- 

 dependence. I am therefore having the above measurements (with 

 slight necessary variation) recorded at my anthropometric laboratory 

 for the purpose of doing so. This laboratory, I may add, is now 

 open to public use under reasonable restrictions. It is entered 

 from the Science Collections in the Western Galleries at South 

 Kensington. 



Mechanical Selector. — Feeling the advantage of possessing a method 

 of classification that did not proceed upon hard and fast lines, I con- 

 trived an apparatus that is quite independent of them, and which I 

 call a mechanical selector. Its object is to find which set, out of a 

 standard collection of many sets of measures, resembles any one given 

 set within any given degree of unlikcness. No one measure in any 

 of the sets selected by the instrument can differ from the corresponding 

 measure in the given set by more than a sj^ecified value. The 

 apparatus is very simple ; it apj^lies to sets of measures of every 

 description, and ought to act on a large scale as well as it does on a 

 small one, with great rapidity, and be able to test several hundred sets 

 by each movement. It relieves the eye and brain from the intolerable 

 strain of tediously comparing a set of many measures with each of a 

 larf^e number of successive sets, in doing which a mental allowance 

 has to be made for a plus or minus deviation of a specified amount in 

 every entry. It is not my business to look after prisoners, and I do 

 not fully know what need may really exist for new methods of quickly 

 identifying suspected persons. If there be any real need, I should 



