Action of Badium Salts on Glass. 
359 
the ends and kept in place by a little cedar oil. The two tubes were 
mounted side by side in a cork and photographed together, a Zeiss micro- 
planar lens being used for the purpose. 
Fig. 1 shows the two pieces of pink glass, and Fig. 2 the green. The 
dark patches in the left-hand tube in Fig. 2 are due to refraction at cracks 
in the glass. In Fig. 1 it can be seen that a dark zone is formed close to 
the bore of the tube, while in Fig. 2 the darkening extends to a greater 
distance without being so intense in any place. The real intensity of the 
colouration, as seen visually, is not correctly indicated by the photographs. 
The magnifications are about 1-1 for the pink tube and 1-5 for the 
green tube. 
Fig. 3. 
M = 3-5 Diameters. 
On submitting No. 1 to a magnification of about 12 diameters a very 
remarkable appearance presented itself. The colouration was seen to 
have proceeded in a series of zones, one zone being clearly marked off 
from the rest, as shown in Fig. 3. Considerable difficulty was experienced 
in getting these zones clearly defined in the photograph, but this was 
accomplished at last by aid of isochromatic plates in conjunction with a 
light filter. 
The innermost zone is very dark, while the succeeding zones show a 
gradual fading of the colour, which persists, however, right to the outside 
of the tube. The external diameter of the pink tube was 9'32 mm., 
the internal diameter 4*35 mm., and the thickness of wall 2-48 mm. 
The thickness of the first dark zone was 0*27 mm., and of the second 
0-33 mm. 
