E, Eye-piece: to shield eye and sample from extraneous light while color determinations are being made. Fatigue of retina should be avoided.
G, Gear: actuates cat’s-eye shutter, which controls amount of light admitted to right half of instrument. Its shaft carries index-hand over dial.
H, Field-Holder: retains sample and standard white in same plane, and isolates them. Is hinged upon lower edge, and secured by pivot clamp.
M, Mirror: permits observation of the isolated halves of the holder, bearing standard white and the color to be measured. Should be clean and free from dust on both sides of central partition.
S, Diffusing Screen, placed over front apertures, to evenly distribute the light.
[(66)] When this numbered scale of values is familiar, it serves not only to describe light and dark grays, but the value of colors which are at the same level in the scale. Thus R7 (popularly called a tint of red) is neither lighter nor darker than the gray of N7. A numeral written above to the right always indicates value, whether of a gray or a color, so that R1, R2, R3, R4, R5, R6, R7, R8, R9, describes a regular scale of red values from black to white, while G1, G2, G3, etc., is a scale of green values.
[(67)] This matter of a notation for colors will be more fully worked out in [Chapter VI.], but the letters and numerals already described greatly simplify what we are about to consider in the mixture and balance of colors.
Mixture of light hues with dark hues.
