250 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
complementaries, the white does not shift into a more or less distinct 
blue, and therefore disappear as white. 
i. Later experiments on thin sections have proved that the fine 
lines at equal distances which belong to the whites do not as a rule 
exceed three, and that, apart from the transparent intervals behind 
the mirror zone, the spaces between the lamine are filled with a 
diffuse precipitate. Under these conditions the interference action 
of such laminz must be nil, even if the incident hght reaches them. 
k. Finally, spectroscopic examination of the pure whites shows : 
continuous image without gaps, which is more or less similar to the 
continuous spectrum from a white object. What is the difference, 
asks the author, between his and Lehmann’s spectral examination ? 
The author thinks that Lehmann did not test pure brilliant whites, 
as obtained by intensification on slow, fine-grained plates, but the 
half-white with a bluish or violet tinge, which usually appears in 
fast plates without intensification.* This pseudo-white, when exam- 
ined in the benzole tank, appears somewhat better, but can never be 
compared with the white obtained by Lippmann, Neuhauss, and the 
author under the stated conditions—that is, treatment with sublimate 
and an amidol developer after weak development. This assump- 
tion appears to be all the more likely as the author’s spectroscopic 
examination of the dirty gray on quick plates without intensification, 
as in Kranseder’s plates, made according to Lehmann’s formula,’ 
shows that the spectrum actually does possess maxima. 
The author was never able to obtain satisfactory colors before he 
learned how to intensify, but since then he has obtained whites, in 
all sorts of subjects, which are purer and more vigorous than in the 
best black and white photograph. 
e 
ANALYSIS OF THE GRAY AND DARK PARTS. 
The dark tones, or those mixed with black, are dependent, accord- 
ing to theory, on the fineness and transparency of the lamine. If, 
for instance, we examine a dark green, as in fig. 16, we shall see that 
the mirror is quite absent, and that in its place is a colorless plane. 
Noteworthy also is the small number of lamine, only four or five, 
and especially their extraordinary transparency and lght yellow 
color. In many cases the lamine appear to consist of a single row 
of yellowish grains. The intervals are clean, comparatively large, 
and quite free from precipitate. Under such conditions it is obvious 
7As a matter of fact Lehmann states in his book that he never intensifies. 
’'The author’s experiments with Lehmann’s plates with the special filter have 
given excellent results as regards speed and color rendering. All attempts to 
obtain a good white were failures. Further, the colors are somewhat dead- 
looking. 
