ious helium. These
same remarkable lines have in more recent years also been detected in
the spectra of various stars.

This gas so long known in the heavens was at last detected on earth. In
April, 1895, Professor Ramsay, who with Lord Rayleigh had discovered the
new element argon, detected the presence of the famous helium line in
the spectrum of the gas liberated by heating the rare mineral known as
cleveite, found in Norway. Thus this element, the existence of which had
first been detected on the sun, ninety-three million miles away, has at
last been proved to be a terrestrial element also.

When it was announced by Runge that the principal line in the spectrum
of the terrestrial helium had a faint and very close companion line on
the red-ward side, some doubt seemed at first to be cast on the identity
of the new terrestrial gas discovered by Ramsay with the helium of the
chromosphere. The helium line of the latter had never been noticed to be
double. Subsequently, however, several observers provided with very
powerful instruments found that the famous line in the chromosphere
really had a very faint companion line. Thus the identity between the
celestial helium and the gas found on our globe was established in the
most remarkable manner. Certain circumstances have seemed to indicate
that the new gas might possibly be a mixture of two gases of different
densities, but up to the present this has not been proved to be the
case.

After it had been found possible to see the spectra of prominences
without waiting for an eclipse, Sir W. Huggins, in an observation on the
13th of February, 1869, successfully applied a method for viewing the
remarkable solar objects themselves instead of their mere spectra in
full sunshine. It is only necessary to adjust the spectroscope so that
one of the brightest lines--_e.g._ the red hydrogen line--is in the
middle of the field of the viewing telescope, and then to open wide the
slit of the spectroscope. A red image of the prominence will then be
displayed instead of the mere line. In fact, when the slit is opened
wide, the prisms produce a series of detached images of the prominence
under observation, one for each kind of light which the object emits.

We have spoken of the spectroscope as depending upon the action of glass
prisms. It remains to be added that in the highest class of
spectroscopes the prisms are replaced by ruled gratings from which the
light is reflected. The effect