ead out in the
manner of a fan, presenting on the screen the following arrangement of
colors: red, orange, yellow, green, blue, indigo and violet.

This order of colors, beginning with red, starts from that side of the
spectrum which is least bent from the right line in which the white
ray was traveling. The violet rays are most bent. The red rays are
thus said to be at the _lower_ edge of the prism, and the violet rays
at the _upper_ edge. Below the red rays there are now known to be
certain invisible rays, as of heat and electricity. Above the violet
rays are other invisible rays, such as the actinic influence. In fact,
the spectrum, beginning invisibly, passes by way of the visible rays
to the invisible again. Nor can any scientist in the world say at the
present time _how much_ is really included in the spread-out fan of
analyzed sunlight.

Thus much scientists have known for some time. Certain other facts,
however, in connection with the solar spectrum are of greater
importance than are its more sensible phenomena. It was in the year
1802 that the English physicist, William Hyde Wollaston, discovered
that the solar spectrum is crossed with a large number of _dark
lines_. He it was who first mapped these lines and showed their
relative position. He it was also who discovered the existence of
invisible rays above the violet. Twelve years afterward Joseph von
Fraunhofer, of Munich, a German optician of remarkable talents, took
up the examination of the Wollaston lines, and by his success in the
investigation succeeded in attracting the attention of the world.

This second stage in scientific discovery is generally that which
receives the plaudits of mankind. It was so in the case of Fraunhofer.
His name was given to the dark lines in the solar spectrum, and the
nomenclature is retained to the present time. They are called the
"Fraunhofer lines." It was soon discovered that the lines in question
as produced in the spectrum are due to the presence of gases in the
producing flame or source of light. It was also discovered that each
substance in, the process of combustion yields its own line or set of
lines. These appear at regular intervals in the spectrum. When several
substances are consumed at the same time; the lines of each appear in
the spectrum. The result is a _system_ of lines, becoming more and
more complex as the number of elements in the consuming materials is
increased.

The lines in a narrow spectrum f