> THEORY OF STATISTICS,
apparatus consists of a funnel opening into a space—say a § inch in
depth— between a sheet of glass and a back-board. This space is
broken up by successive rows of wedges like 1, 2 3, 4 5 6, etc., which
will divide up into streams any granular material such as shot or
mustard seed which is poured through the funnel when the
apparatus is held at a slope. At the foot these wedges are
replaced by vertical strips, in the spaces between which the
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Fie. 48.—The Pearson-Galton Binomial Apparatus.
material can collect. Consider the stream of material that
comes from the funnel and meets the wedge 1. This wedge 1s
set so as to throw ¢ parts of the stream to the left and p parts
to the right (of the observer). The wedges 2 and 3 are set so as
to divide the resultant streams in the same proportions. Thus
wedge 2 throws ¢2 parts of the original material to the left and
gp to the right, wedge 3 throws pg parts of the original material
to the left and p? to the right. The streams passing these wedges
are therefore in the ratio of ¢2: 2gp: p2. The next row of wedges
is again set so as to divide these streams in the same proportions

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