> 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 
298