342 E. L. Nichols—A. Study of Pigments. 
Art, XLI.—A Spectro-photometric Study of Pigments ; by 
Epwarp L. NicHous, Ph.D. 
[Read at the Philadelphia meeting of the American Association for the Advance- 
ment of Science. ] 
THE usual methods of determining the three so-called con- 
stants of colur—hue, purity and luminosity—are open to serious 
question. If the light reflected by pigments were nearly 
monochromatic, the comparison of their colors with the tints of 
the solar spectrum would offer no difficulty and the wave-length 
would afford a most convenient measure of the hue. The 
the resemblance is increased. The purity of the pigment 1s 
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