The men of science had long before analyzed the sunlight. They had
broken it up into the rays of different color that together make
the white light we see. Any boy can do it with a prism, and in the
band or spectrum of red, yellow, green, blue, and violet that then
appears, he has before him the cipher that holds the key to the
secrets of the universe if we but knew how to read it aright; for
the sunlight is the physical source of all life and of all power.
The different colors represent rays with different wave-lengths;
that is, they vibrate with different speed and do different work.
The red vibrate only half as fast as the violet, at the other end of
the spectrum, and, roughly speaking, they are the heat carriers. The
blue and violet are cold by comparison. They are the force carriers.
They have power to cause chemical changes, hence are known as the
chemical or actinic rays. It is these the photographer shuts out of
his dark room, where he intrenches himself behind a ruby-colored
window. The chemical ray cannot pass that; if it did it would spoil
his plate.
This much was known, and it had been suggested more than once that
the "disinfecting" qualities of the sunlight might be due to the
chemical rays killing germs.
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