248 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
a long time and the finer lines are nearer to the surface, the different 
thickness and distance of the laminz must be ascribed to the registra- 
tion of different waves. Neither with compound colors nor pure 
white are all spectrum waves to be distinguished. 
Bluish, reddish, and greenish white have a similar structure; all 
these colors show with the mirror zone a laminar system and their 
optical effect is added to the reflection from the mirror zone. 
For the chromatic interference, as with pure colors, only the two 
first—or, as noted above, in the case of a fine secondary strip (fig. 
lic) the three first laminee—are used. The color thus formed is 
weakened by the somewhat disturbing reflection of white from the 
mirror zone. That the surface film, in spite of its paucity in precipi- 
tate, causes weakening of the color is proved by rubbing or scraping 
the plate, for then the whitish tinge disappears and the dominant 
color appears much more strongly, and if the scraping is continued 
it is shifted toward the more refrangible end. 
After the author’s views as above had been published, he heard 
of Lehmann’s work on the same subject, but the results of the two 
workers are not in agreement. 
According to Lehmann, white is formed not, as assumed by Lipp- 
mann, by the confusion of the incident light of various vibrations 
from the lamine, but by reflection from two lamine correspond- 
ing to complementary colors. As proof of this. assumption, Leh- 
mann advances (1) the possibility of obtaining photo-micrographs 
under special experimental conditions of the registration of two syn- 
chronous waves; (2) the spectroscopic examination of the light re- 
flected from the whites of a picture placed in a benzole tank. In 
the latter case he observed that the whites of the picture did not, as 
the whites in nature, emit a continuous spectrum, but a discontinu- 
ous one, or a continuous spectrum with two or three distinct maxima 
preponderating. From this Lehmann concludes, in agreement also 
with Pfaundler,* that the plates do not possess the power of regis- 
tering simultaneously a greater number of waves of varying vibra- 
tion, but only two or three, and he explains the formation of white 
and gray by the well-known property of the retina of synthesizing to 
white when two complementary colors act on the rods. 
In principle this coincides with the author’s conclusions as to the 
formation of two kinds of lamine; but the question does not appear 
to the author to be experimentally proved, for, as will be seen later, 
the deeper lying laminz do not, or only in rare cases, help to produce 
the colors. 
Lehmann’s conclusions have caused the author to repeat his experi- 
ments, and he comes to the conclusion that brillant whites are due 
“Prude’s Annalen, 1904. See also “B. J.,’’ October 12, 1906, p. SOT. 
