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light, but by duly strengthening the precipitate you may
render the white light of noon as ruby-colored as the sun
when seen through Liverpool smoke, or upon Alpine hori-
zons. I do not, however, point to the gross smoke arising
from coal as an illustration of the action of small particles,
because such smoke soon absorbs and destroys the waves
of blue instead of sending them to the eyes of the observer.

These multifarious facts, and numberless others which
cannot now be referred to, are explained by reference to
the single principle, that where the scattering particles are
small in comparison to the size of the waves we have in
the reflected light a greater proportion of the smaller
waves, and in the transmitted light a greater proportion
of the larger waves, than existed in the original white
light. The physiological consequence is that in the one
light blue is predominant, and in the other light orange
or red. And now let us push our inquiries forward.
Our best microscOpes can readily reveal objects not more
than math of an inch in diameter. This is less than
the length of a wave of red light. Indeed, a first-rate
microscope would enable us to discern objects not exceed-
ing in diameter the length of the smallest waves of the
visible spectrum. By the microscope, therefore, we can
submit our particles to an experimental test. If they are
as large as the light-waves they will infallibly be seen:
and if they are not seen it is because they are smaller. I
placed in the ,hands of our President a bottle containing
Brflcke’s particles in greater number and coarseness than
those examined by Brucke himself. The liquid was a
milky blue, and Mr. Huxley applied to it his highest
microscopic power. He satisfied me at the time that had
particles of even figmth of an inch in diameter existed
in the liquid they could not have escaped detection. But
no particles were seen. Under the microscope the turbid
liquid was not to be distinguished from distilled water.


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