8 in.

about 4000.[40] [40] This figure is adapted (by the kind permission of the publishers) from one given in Professor K.Pearson's _Chances of Death_, vol.i.

p.
277.

For the relation between such records of actual observation and the curves resulting from mathematical calculation of known causes of variation, see _ibid._, chap, viii., the paper by the same author on 'Contributions to the Mathematical Theory of Evolution,' in vol.186 (A) of the _Royal Society's Philosophical Transactions_ (1896), and the chapters on evolution in his _Grammar of Science_, 2nd edition.
Such figures, when they simply record the results of the fact that the likeness of the offspring to the parent in evolution is constantly inexact, are (like the records of other cases of 'chance' variation) fairly symmetrical, the greatest number of instances being found at the mean, and the descending curves of those above and those below the mean corresponding pretty closely with each other.

Boot manufacturers, as the result of experience, construct in effect such a curve, making a large number of boots of the sizes which in length or breadth are near the mean, and a symmetrically diminishing number of the sizes above and below it.
In the next chapter I shall deal with the use in reasoning of such curves, either actually 'plotted' or roughly imagined.