14 shot, let us say, or by mixing with the No.

10 a few very large bullets.

Which is actually the case would be shown only by the examination of the individual cases.

This is usually done by comparing each case with the average of the whole lot, and taking the average of the differences thus secured--a quantity called the "mean variation." In the case of the experiments with the squares, the errors in the judgments of the students were found to lie always in one direction.
The answers all tended to show that they took, for the one originally shown, a square which was really too large.

Casting about for the reason of this, it was considered necessary to explain it by the supposition that the square remembered had in the interval become enlarged in memory.