prediction, after its three-quarters of a century of voyaging
but in the abyss of space. Proved thus to bow to
natural law, the celestial messenger could no longer
fully, sustain its role. But long-standing notoriety cannot
be lived down in a day, and the comet, though
proved a "natural" object, was still regarded as a very
menacing one for another hundred years or so. It remained
for the nineteenth century to completely unmask
the pretender and show how egregiously our forebears
had been deceived.

The unmasking began early in the century, when Dr.
Olbers, then the highest authority on the subject, expressed
the opinion that the spectacular tail, which had
all along been the comet's chief stock-in-trade as an
earth-threatener, is in reality composed of the most
filmy vapors, repelled from the cometary body by the
sun, presumably through electrical action, with a velocity
comparable to that of light. This luminous suggestion
was held more or less in abeyance for half a
century. Then it was elaborated by Zollner, and
particularly by Bredichin, of the Moscow observatory, into
what has since been regarded as the most plausible of
cometary theories. It is held that comets and the sun
are similarly electrified, and hence mutually repulsive.
Gravitation vastly outmatches this repulsion in the
body of the comet, but yields to it in the case of gases,
because electrical force varies with the surface, while
gravitation varies only with the mass. From study of
atomic weights and estimates of the velocity of thrust