Page:Method for constructing the natural scale of pure color (Nutting, 1909).djvu/16

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The ordinates of the curve of color as a function of wave length are given in the last column. They were obtained by integration of the sensibility curve, the partial areas (divided by two on the scale of the figure) being given in the fourth column. Bach number in the last column is the sum (divided by lo) of the ordinate areas of the fourth column added from the bottom to and including that wave length. The color-wave length curve is plotted in the figure.

A difference of one unit in the color scale represents a difference in color that is just easily perceptible, hence forms a convenient natural unit, although any other subdivision might be used. In Fig. I, each unit of the color scale is indicated on the wave-length axis and just above are indicated roughly the positions of six spectral hues.

To test the theoretical color curve, a normal spectrum was projected on a black screen in which had been cut slits spaced according to the wave lengths of the color units, the slits being covered with ground glass. No departure from uniformity in the color steps could be detected by the ten or more individuals who carefully examined them.

The wave lengths of each of these color steps is given in Table III.

These computations have been carried through merely to illustrate the method. They may easily be made for any eye for which the sensibility curve is known.

If the sensibility curves of a large number of subjects were known, the properties of an average normal human eye might be deduced and a scale of color constructed and adopted.