ely held of "moral" qualities. Men are
considered to be equally responsible for their conduct, and failure to
conform to the accepted code in this respect brings punishment. It is
sometimes conceded that men have had differing opportunities to learn
the principles of morality; but given equal opportunities, it is almost
universally held that failure to follow the principles indicates not
inability but unwillingness. In short, public opinion rarely admits that
men may differ in their inherent capacity to act morally.

In view of its almost universal and unquestioned, although half
unconscious, acceptance as part of the structure of society, it becomes
of the utmost importance that this doctrine of human equality should be
examined by scientific methods.

Fortunately this can be done with ease. Methods of mental and physical
measurement that have been evolved during the last few decades offer
results that admit of no refutation, and they can be applied in hundreds
of different places.

[Illustration: DISTRIBUTION OF 10-YEAR-OLD SCHOOL CHILDREN

FIG. 8.--The graph shows that 10-year-old children in
Connecticut (1903) are to be found in every grade, from the first to the
eighth. The greatest number is in the fourth grade, and the number who
are advanced is just about the same as the number who are retarded.]

It will not be worth while to spend any time demonstrating that all
individuals differ, at birth and during their subsequent life,
physically. The fact is patent to all. It carries with it as a necessary
corollary mental differences, since the brain is part of the body;
nevertheless, we shall demonstrate these mental differences
independently.

We present in Fig. 8 a graph from E. L. Thorndike, showing the number of
10-year-old children in Connecticut (1903) in each school grade. If the
children are all intellectually equal, all the 10-year-olds ought to be
in the same grade, or near it. Numerous explanations of their wide
distribution suggest themselves; as a working hypothesis one might adopt
the suggestion that it is because the children actually differ in innate
ability to the extent here indicated. This hypothesis can be tested by
a variety of mental measurements. S. A. Courtis' investigation of the
arithmetical abilities of the children in the schools of New York City
will be a good beginning. He measured the achievements of pupils in
responding to eight tests, which were believed to give a fair idea of
th