*THE POPULAR SCIENCE MONTHLY.*

dents, is a good example. In all cases the distribution closely approximates the normal type.

Does the distribution of the complex abilities that determine excellence in college courses approximate this normal type? Theoretically it should, and our theory is supported in a striking way by the distribution of 8,969 grades in twenty-one elementary courses for two years, 1907-08, at Harvard College. The curve in Fig. 11, representing this distribution, is nearly normal. The percentages for the grades A-E are, respectively, 7, 20, 42, 21, 7. Yet there are wide variations among

the instructors in these very courses. In fact not a single instructor came as near to a normal distribution as the sum of all their grades. Now, no one of these markers is as likely to tell the truth as all together. Their several errors correct each other and thus give us, in Fig. 11 (Group 1), a close approximation to the type of curve we should expect to have with an infinite number of cases. In 1909-10, the grades in certain elementary courses in Harvard College (Chemistry 1, Comparative Literature 1, English A, Government 1, History 1, Mathematics F, Philosophy C, Zoology 1) were distributed in the following percentages: A = 5.5, B = 21, C = 44, D = 19.5, E = 9.