188 C. H. Koyl— Colors of Thin Blowpipe Deposits. 
repetition of the test then showed that the proportion of light 
polarized by the layer of carbon, at the given angle, was almost 
nothing; that by the thick white coating, small; while on the 
blue the phenomenon was almost complete. What light here 
was not polarized was evidently reflected from the larger parti- 
cles mixed with the fine, for the analyzer, while it did not 
totally extinguish the light, yet excluded nearly all appearance 
of blueness. 
In order to determine the character of the transmitted light, 
a microscope covering-glass was inlaid in the charcoal and the 
oxidation so executed that the glass was in the center of a 
small area all of which was blue. On removing the glass, the 
light which passed through, proved to be of the expected 
yellow, though less brilliant than anticipated. The color 
might be seen either by transmitting the direct light of the sun 
or by placing the glass at such an angle that total reflection 
was produced and thus in the passage of the rays through the 
layer to the glass and out through the layer to the eye the 
blue was principally lost and only the mixture of longer rays 
appeared. Viewed through a microscope, the result was the’ 
same. I have since, however, improved upon this plan by the 
more convenient method of covering with carbon a piece of 
ordinary window-glass, three inches by two, and then project- 
ing the oxide upon the opposite surface of the plate. There is 
thus no difficulty in distinguishing a very slight amount of 
color in the coating and for transmitted light, any portion of 
the carbon may be easily removed. 
color (dark red) through yellow into a fine green. As before, 
the light reflected from the thin layers is highly polarized and 
the rays which pass through form a deep, dark red. In excep- 
tional cases, it is possible to produce such a thin coating that 
the extreme edge is fringed with a faint blue. 
