Thus a series of arrays of beech leaves, gathered, subject to the precautions indicated, from each of loo beech trees in Buckinghamshire by Professor Pearson, gave 16.1 as the mean number of veins per leaf, the standard deviation of the veins in the series being 1.735.

After a large series of measurements, involving the most varied characters of human brothers, Pearson has shown that the correlation has a value very nearly equal to z; so that the variability of human children obeys the same law as that of other repeated structures, the standard deviation of an array, produced by the same parents, having an average value equal to the standard deviation of the whole filial generation multiplied by 1 2 1 J I - (or by.

Shull (American Naturalist, xxxvi., 1902), the mean number of bracts, ray-florets and discflorets, and the standard deviation of each, was determined on four different days, with the following result: TABLE III.

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But obviously the information given by the standard deviation is limited: the frequency of movement cannot be inferred from it; two series might have quite different average oscillations and yet the same standard deviation; and the range of movement, or spread of the variations from the average price (though allowed for in the standard deviation more than in the average error), is hidden.