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x 88o.J Analyses of Books. 
blue and through gamboge, and allow it to fall upon a prism. 
We shall find the specftra thus obtained very different from that 
of white light. In that of gamboge, the violet, ultramarine, and 
a portion of the blue are cut off. In the speftrum of the Prussian 
blue, the red, orange, and yellow are cut off. Now every ray of 
lig-ht that falls upon a mixture of these two pigments undergoes 
this double process in the particles from which it is transmitted 
and refledted, and the result of the subtraction process is that 
green remains. But if we throw the blue portion of one spedtrum 
of white light upon the yellow portion of another, we have a 
process of addition, not subtraction, and the result is a grayish 
white. From modern researches it appears that if we leave pig- 
ments out of the question, and attend to colours in the simple 
sense of the word, the three fundamentals are red, green, and a 
blue-violet. 
The author’s classification of colours is different from the cele- 
brated circles of Prof. Chevreul. His arrangement is represented 
by a cone, on the base of which are arranged in a circle the fol- 
lowing colours : — Carmine, vermillion, orange, yellow, yellowish 
green, green, bluish green, turquoise, ultramarine, bluish violet, 
purplish violet, and purple. All these colours, it will be observed, 
are prismatic except “ purple.” This name the author gives to 
a colour which is not found in the spedtrum, but which would 
form the intermediate gradations between carmine and violet. 
It coincides tolerably with that of the dye-ware commonly known 
as magenta, but technically called rosanilin acetate. If we then 
place white in the centre of this circle, all the gradations between 
it and the above twelve colours can be arranged in lines running 
from the centre to the circumference. Here therefore will be the 
places of such colours as rose, pink, peach, lilac, and lavender, 
which are respectively dilutions of carmine and of the various 
grades of purple and violet. 
Again, at the apex of the cone we place black. On lines 
ranging along the exterior surface of the cone, from the base to 
the apex, are arranged such colours as olive (a green saddened 
with black), the browns (which according to their various nature 
may be either yellowish green, yellow, or red saddened in a 
similar manner), wine-colour (which may be called a blackened 
purple), &c. The true greys — i.e ., the gradations from white to 
black — fall along the line passing from the centre of the base to 
the apex. 
In the fourth chapter the author deals with the theory of con- 
trast — a subject based almost entirely upon physiological consi- 
derations. A number of easy and familiar experiments prove 
that any coloured objeCt, if regarded fixedly for some little time, 
causes the observer, on turning away, to see its image, but 
changed to the complementary colour. Thus after looking at a 
red wafer placed upon a sheet of white or grey paper, we fancy 
we see a bluish green circle of a similar size to the wafer. But 
