--Print of a finger-tip showing a loop-pattern,
enlarged about eight times. This is a common type of pattern, and at
first glance the reader may think it could be mistaken for one of his
own. There are, however, at least sixty-five "ridge characteristics" on
the above print, which an expert would recognize and would use for the
purpose of identification. If it were found that the first two or three
of them noted corresponded to similar characteristics on another print,
the expert would have no doubt that the two prints were made by the same
finger. In police bureaus, finger-prints are filed for reference with a
classification based on the type of pattern, number of ridges between
two given points, etc.; and a simple formula results which makes it easy
to find all prints which bear a general resemblance to each other. The
exact identity or lack of it is then determined by a comparison of such
_minutiae_ as the sixty-five above enumerated. While the general outline
of a pattern is inherited, these small characters do not seem to be, but
are apparently rather due to the stretching of the skin as it grows.
Illustration from J. H. Taylor.]

[Illustration: DISTRIBUTION OF I Q'S OF 905 UNSELECTED CHILDREN, 5-14
YEARS OF AGE

THE DISTRIBUTION OF INTELLIGENCE

FIG. 23.--Diagram showing the mentality of 905 unselected
children, 5 to 14 years of age, who may probably be taken as
representative of the whole population. The median or tallest column,
about one-third of the whole number, represents those who were normal
or, as a statistician would say, mediocre. Their mental ages and
chronological ages were practically identical. To the left of these the
diminishing columns show the number whose mental ages fell short of
their chronological ages. They are the mentally retarded, ranging all
the way down to the lowest one-third of one per cent who represent a
very low grade of feeble-mindedness. On the other side the mentally
superior show a similar distribution. A curve drawn over the tops of the
columns makes a good normal curve. "Since the frequency of the various
grades of intelligence decreases _gradually_ and at no point abruptly on
each side of the median, it is evident that there is no definite
dividing line between normality and feeble-mindedness, or between
normality and genius. Psychologically, the mentally defective child does
not belong to a distinct type, nor does the genius.... The common
opinion that extreme deviation