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.
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