Page:Popular Science Monthly Volume 63.djvu/391

Rh definite though arbitrary limits, themselves the result of much experience ill measurements, and designed to divide any average set of measurements into three approximately equal divisions, rather than to divide equally the range of millimeters between the extremes of a given measurement. Thus, to quote an example furnished, "the numerical limits of the 'medium' head-length as used at the Prefecture of Police in Paris include an interval of but G millimeters (185-190), while those included under 'large' extend from 191 mm. to the greatest dimensions possible, an extent of more than three centimeters."

Now if we were to conceive of each one of these eleven measuremenfs as varying independently of one another and as being divided into three subdivisions, the number of possible subdivisions under which individual anthropometric records could be filed would reach the large number of 3 to the 11th power, or 177,147, but in practical use M. Bertillon employs for purposes of identification only a few of these measurements, which he gives in the work just quoted, together with an hypothetical application, as follows:

He supposes the case of 90,000 sets of measurements, a number approximately corresponding to that of the adult male prisoners recorded in the Paris prisons up to 1893. Of these the first classification is made by means of the length of head, and as the subdivisions, small, medium and large, are fixed with reference to equality of division, approximately 30,000 of these records will be placed in each.

Each of these subdivisions is now divided again into three parts, in accordance with the breadth of head, a division which leaves approximately 10,000 in each of the nine compartments, i. e., 10,000 individuals whose head length and head breadth fall into the same categories. The third division, which reduces the number of records in each of 27 compartments to about 3,300, is based upon the length of the left middle finger, and the fourth, resulting in 1,100 in each of the 81 compartments, is based upon the length of the left foot. The length of the cubitus then follows, which increases the number of compartments to $$243 (=3^5)$$ and the number of individual cases in a compartment to less than 400. By the addition of the standing height, the number of compartments is increased to $$729 (=3^6)$$ and that of the cases in each compartment to approximately 130, and these numbers become respectively $$2187 (=3^7)$$ and 42 by the use of measurements taken from the left little finger. These are finally reduced to small sets of a dozen records each by such criteria as the color of the eye and the length of the right ear, after which this small number may be carefully compared for individual measurements.

With some modifications the above system is in official use in most of the civilized countries of the world, including England, Russia,