Sse is lel nig CR a la ea 
M. M. Garver— Voluntary Nervous Action, etc. 189 
The other case, lead, is now easily explained. This metal 
gives a coating of which the color is a beautiful chrome 
yellow, and regarding this merely as a repetition of the preced- 
ing phenomenon and the yellow as compounded of rays from 
the whole range of the spectrum but not in the proper propor- 
tion to form white, the line of thought suggested evidently is, 
that if*the layer be decreased in thickness regularly from the 
center to the circumference of the charcoal, there ought to be, at 
some distance from the centre, a zone within which sufficient 
red should be transmitted to equalize the amount of blue lost 
by absorption and the reflected rays should form a yellowish 
white. Beyond this, as the thickness of layer still decreased, 
the color should be blue for the same reason as in the case of 
antimony. The white zone is easily produced and the blue 
border, which always surrounds it, polarizes the light as before 
and transmits orange colored rays. 
e theory, once given, serves to explain nearly all the 
anomalous colorings of the charcoal coatings ;—the bluish 
a change in reflecting power could have been produced by so 
small a change in size and thickness. 
Baltimore, Md., July 9, 1880. 
Arr. XXIV.—The Periodic Character of Voluntary Nervous 
Action; by M. M. GARVER. 
In the June number of this Journal for 1878 (No. 90, vol. 
XV, 18-422), in an article on Nervous Transmission, I 
