in producing
them; Kiaer somewhat obscurely explains them through the evolution of
gases by colliding particles;[1278] Herz of Vienna concludes tails to be
mere illusory appendages produced by electrical discharges through the
rare medium assumed to fill space.[1279] But Hirn[1280] conclusively
showed that no such medium could possibly exist without promptly
bringing ruin upon our "daedal earth" and its revolving companions.

On the whole, modern researches tend to render superfluous the chemical
diversities postulated by Bredikhine. Electricity alone seems competent
to produce the varieties of cometary emanation they were designed to
account for. The distinction of types rests on a solid basis of fact,
but probably depends upon differences rather in the mode of action than
in the kind of substance acted upon. Suggestive sketches of electrical
and "light-pressure" theories of comets have been published respectively
by Mr. Fessenden of Alleghany,[1281] and by M. Arrhenius at
Stockholm.[1282] Although evidently of a tentative character, they
possess great interest.

Bredikhine's hypothesis was promptly and profusely illustrated. Within
three years of its promulgation, five bright comets made their
appearance, each presenting some distinctive peculiarity by which
knowledge of these curious objects was materially helped forward. The
first of these is remembered as the "Great Southern Comet." It was never
visible in these latitudes, but made a short though stately progress
through southern skies. Its earliest detection was at Cordoba on the
last evening of January, 1880; and it was seen on February 1, as a
luminous streak, extending just after sunset from the south-west horizon
towards the pole, in New South Wales, at Monte Video, and the Cape of
Good Hope. The head was lost in the solar rays until February 4, when
Dr. Gould, then director of the National Observatory of the Argentine
Republic at Cordoba, caught a glimpse of it very low in the west; and on
the following evening, Mr. Eddie, at Graham's Town, discovered a faint
nucleus, of a straw-coloured tinge, about the size of the annular nebula
in Lyra. Its condensation, however, was very imperfect, and the whole
apparition showed an exceedingly filmy texture. The tail was enormously
long. On February 5 it extended--large perspective retrenchment
notwithstanding--over an arc of 50 deg.; but its brightness nowhere
exceeded that of the Milky Way in Taurus. There was little