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point. Those waves are absorbed whose vibrations syn-
chronize with those of the molecules or atoms on Which
they impinge; a principle which is sometimes expressed by
saying that bodies radiate and absorb the same rays. This
great law, as you know, is the foundation of spectrum-
analysis; it enabled Kirchhoff to explain the lines of Frauen-
hofer, and to determine the chemical composition of the
atmosphere of the sun. If, then, after such a change as
that involved in the passage of a vapor to the liquid state,
the same waves are absorbed as were absorbed prior to the
passage, it is a proof that the molecules, which must have
utterly changed their periods, cannot be the seat of the ab-
sorption; and we are driven to conclude that it is to the
atoms, whose rates of vibration are unchanged by the
change of aggregation, that the wave-motion is transferred.
If experiment should prove this identity of action on the
part of a vapor and its liquid, it would establish in a new
and striking manner the conclusion to which We have pre-
viously leaned.

We will now resort to the experimental test. In front
of this experimental tube, which contains a quantity of the
nitrite-offamyl vapor, is placed a glass cell a quarter of an
inch in thickness, filled with the liquid nitrite of amyl. I
send the electric beam first through the liquid and then
through its vapor. The luminous power of this beam is
very great, but it can make no impression upon the vapor.
The liquid has robbed it completely of its effective waves.
When the liquid is removed chemical action immediately
commences, and in a moment we have the apparently
empty tube filled with this bright cloud, precipitated by
one portion of the beam, and illuminated by another. Thus
we uncover to some extent the Secrets of this world of
molecules and atoms.

Instead of employing air as the vehicle by which the
vapor is carried into the experimental tube, we may em-

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