and
was, indeed, indispensable. For a luminous point, such as a star
appears, becomes, when viewed through a prism, a variegated line, which,
until broadened into a band by the intervention of a cylindrical lens,
is all but useless for purposes of research. This process of _rolling
out_ involves, it is true, much loss of light--a scanty and precious
commodity, as coming from the stars; but the loss is an inevitable one.
And so fully is it compensated by the great light-grasping power of
modern telescopes that important information can now be gained from the
spectroscopic examination of stars far below the range of the unarmed
eye.

The effective founders of stellar spectroscopy, then (since Rutherfurd
shortly turned his efforts elsewhither), were Father Secchi, the eminent
Jesuit astronomer of the Collegio Romano, where he died, February 26,
1878, and Sir William Huggins, with whom the late Professor W. A. Miller
was associated. The work of each was happily directed so as to
supplement that of the other. With less perfect appliances, the Roman
astronomer sought to render his extensive rather than precise; at Tulse
Hill searching accuracy over a narrow range was aimed at and attained.
To Father Secchi is due the merit of having executed the first
spectroscopic survey of the heavens. Above 4,000 stars were passed in
review by him, and classified according to the varying qualities of
their light. His provisional establishment (1863-67) of four types of
stellar spectra[1369] has proved a genuine aid to knowledge through the
facilities afforded by it for the arrangement and comparison of rapidly
accumulating facts. Moreover, it is scarcely doubtful that these
spectral distinctions correspond to differences in physical condition of
a marked kind.

The first order comprises more than half the visible and probably an
overwhelming proportion of the faintest stars. Sirius, Vega, Regulus,
Altair, are amongst its leading members. Their spectra are distinguished
by the breadth and intensity of the four dark bars due to the absorption
of hydrogen, and by the extreme faintness of the metallic lines, of
which, nevertheless, hundreds are disclosed by careful examination. The
light of these "Sirian" orbs is white or bluish; and it is found to be
rich in ultra-violet rays.

Capella and Arcturus belong to the second, or solar type of stars, which
is about one-sixth less numerously represented than the first. Their
spectra are quite cl