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Screen-Plates — Historical and Theoretical Data 465
the Autochrome plate there are about 4,000,000 starch grains to the square inch, so that the probability of clumping of twelve grains of the same color in a square inch will be 4,000,000/120,000 or 33.3. Therefore, in a square inch we may, if the grains are perfectly mixed and distributed at random, expect to find 33 clumps of twelve grains or over; 11 of thirteen grains or over; 4 of fourteen grains or over, and 1 of fifteen grains or over. There will probably be only 1 clump of seventeen grains in a quarter plate, while a clump of twenty grains should occur about twice in a dozen whole plates. In order to determine the extent to which this calculation applied, the said investigators examined one hundred fields of the plate, each containing about 400 grains, and they found 1 clump of seventeen grains, 1 of sixteen, 3 of fourteen, 5 of twelve, 11 of eleven, 21 of ten and 29 of nine. Numerous counts of other workers practically confirm this statement.
Fig. 116. Red
C. Wolf-Czapek26 found clumps of from three to fifteen grains, and the ratios red 28, green 45, blue 27 per cent. A. Haddon27 found within two given areas red 127 and 116; green 170 and 155; blue 129 and 108, which roughly correspond to 40, 30 and 30 per cent. Ferran28 found 46, 31 and 30 per cent. E. Valenta29 also found 40, 30 and 30. According to A. Seyewetz,30 the grains were not mixed in any definite proportions, but empirically so that no one color predominated, (see also p. 467). In connection with this point Mees and Pledge stated that as the makers were unable to adjust for the fulfillment of the first black condition by the variation of the size of the units, they probably increased the number of the green grains.
The distribution of the starch grains is well shown in Figs. 116, 117,