E. L. Nichols—A Study of Pigments. 347 
given in ten millionths of a millimeter. The first set of values 
given in the table are referred to the corresponding intensities’ 
of the standard spectrum ; the second set are all referred to the 
intensity of the region of the D line in the standard spectrum, 
the well known measurements of the intensities of the solar- 
spectrum by Lamansky’ being used in the reduction. 
The curves (figure 2) accompanying the foregoing table rep- 
resent graphically the results of this method as applied to the 
four pigments in question. e abscissee are wave-lengths, the 
ordinates are intensities and the curves show the distribution 
of energy throughout the prismatic spectrum. They are identi- 
cal with the curves which would be obtained by exploring the 
spectra of the pigments with a sufficiently delicate thermopile, 
and do not represent the optical effect which is a complicated 
function of the energy of the ray, the character of which is not. 
the same for all wave-lengths nor for all eyes. An inspection 
of these curves verifies the opinion expressed in the first para- 
18 practice in associating the sensation of color produced by pig- 
ments with the form of curve representing them. 
_if we retain as the standard of purity the monochromatic 
Unt, the intensity-curve of a perfectly pure color is a vertical 
€ measured by supposing the pigment to consist of a mono- 
chromatic tint plus a certain amount of white light, and that 
1 Lamansky, Poggendorff’s Annalen cxli. 
A 
