258 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
LAMINZE IN PLATES EXPOSED WITHOUT A MERCURY MIRROR. 
The earlier experiments of Krone and the more recent ones of 
Rothé have proved the possibility of obtaming interference colors 
with Lippmann’s plates without using a mercury mirror, The 
pictures thus made have only a faint brilliance, and require, more- 
over, much longer exposures. This is obvious, as the stationary waves 
are formed by interference between the incident light and the few 
light waves which are reflected from the surface between the gelatin 
and the air. The author has repeated the interesting experiment and 
obtained comparatively good results of the shorter wave lengths, 
violet to green; far less satisfactory, however, were the reproduc- 
tions of the red, orange, and yellow. Examination of sections shows 
in all cases the presence of correct lamine, which are few in number, 
however, and are separated by intervals which are not free from 
precipitate. Fig. 17 shows the section through the blue of such 
a result. The lamine, only three or four in all, are composed of 
very fine grains. The second lamina is the best and darkest. In 
the limiting zone there is no precipitate, and this proves therefore 
that, as with the mercury mirror, the surface of the gelatin is 
identical with the first opposite phase plane. 
The whites obtained in this way are also the same as those obtained 
with Lippmann’s method; behind the dense thin mirror zone there 
are some fine laminz, which, deeper down, degenerate into an irreg- 
ular gray deposit. 
CONCLUSIONS. 
From his long and comprehensive researches on the structure of 
the Lippmann heliochromes the author comes to the following con- 
clusions: 
1. As already recognized by Neuhauss, the spectrum colors are 
produced by a series of metallic lamine, separated from one another 
by colorless intervals. These films occupy a third or a half of the 
thickness of the gelatin. Near the free surface they are sharply 
defined and distinctly separate one from the other, the deeper they 
are the more diffuse and indistinct they become. 
2. Between the first laminz and the surface there is generally : 
clear zone, which corresponds to the first opposite phase or null point. 
Frequently through intensification this contracts considerably, or 
completely disappears. 
3. The colors of natural objects give pictures the structure of 
which agrees generally with that of the spectral colors. 
4. The production of white is due to the formation of a dense 
metallic lamina, the mirror zone, with great reflective power, and 
composed of an opaque dark closely compacted precipitate. Then 
