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Tyndall, John, 1820-1893

"Six Lectures on Light Delivered In The United States In 1872-1873"

A trace of
soap in water gives it a tint of blue. London milk makes an
approximation to the same colour, through the operation of the same
cause: and Helmholtz has irreverently disclosed the fact that a blue
eye is simply a turbid medium.

Sec. 12. _Artificial Sky_.
But we have it in our power to imitate far more closely the natural
conditions of this problem. We can generate in air artificial skies,
and prove their perfect identity with the natural one, as regards the
exhibition of a number of wholly unexpected phenomena. It has been
recently shown in a great number of instances by myself that waves of
ether issuing from a strong source, such as the sun or the electric
light, are competent to shake asunder the atoms of gaseous molecules.
The apparatus used to illustrate this consists of a glass tube about a
yard in length, and from 21/2 to 3 inches internal diameter. The gas or
vapour to be examined is introduced into this tube, and upon it the
condensed beam of the electric lamp is permitted to act. The vapour is
so chosen that one, at least, of its products of decomposition, as
soon as it is formed, shall be _precipitated_ to a kind of cloud.


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