colors and projects a band of light called a spectrum. This was known
for three hundred years, and not much thought of it until Fraunhofer
viewed it with a telescope, and was surprised to find it filled with
hundreds of black lines invisible to the unaided eye. Could it be
possible that there are portions of the solar surface that fail to send
out light? Such is the fact, and then began a twenty years' search to
learn the cause. The lines in the solar spectrum were unexplained until
finally metals were vaporized in the intense heat of the electric arc
and the light passed through a spectroscope, when behold the spectra of
metals were filled with bright lines in the same places as were the
dark lines in the spectrum of the sun. Another step: if when metals are
volatilized in the arc, rays of light from the sun are passed through
the vapor and allowed to enter the spectroscope, a great change is
wrought; a reversal takes place, and the original black bands reappear.
A new law of nature was discovered, thus: "Vapors of all elements absorb
the same rays of light which they emit when incandescent." Every element
makes a different spectrum with lines in different places and of
different widths. These have been memorized by chemists, so that when an
expert having a spectroscope sees anything burn he can tell what it is
as well as read a printed page. Men have learned the alphabet of the
universe, and can read in all things radiating light, the constituent
elements. The black lines in the solar spectrum are there because in the
atmosphere of the sun exist vapors of metals, and the light from the
liquid metals below is unable to pass through and reach the earth, being
absorbed kind for kind. Gaseous iron sifts out all rays emitted from
melted iron, and so do the vapors of all other elements in the sun,
radiating light in unison with their own. Sodium, iron, calcium,
hydrogen, magnesium, and many other substances are now known to be
incandescent in the sun and stars; and the results of the developments
of the spectroscope may be summed up in the generalization that all