A Popular History of Astronomy During the Nineteenth Century: Fourth EditionClerke, Agnes M. (Agnes Mary)
History
A Popular History of Astronomy During the Nineteenth Century: Fourth Edition
Clerke, Agnes M. (Agnes Mary)
Astronomy -- History -- 19th century
They were verified by the detection at Rome, August 6, 1835, of a nearly
circular misty object not far from the predicted place of the comet. It
was not, however, until the middle of September that it began to throw
out a tail, which by the 15th of October had attained a length of about
24 degrees (on the 19th, at Madras, it extended to fully 30),[279] the
head showing to the naked eye as a reddish star rather brighter than
Aldebaran or Antares.[280] Some curious phenomena accompanied the
process of tail-formation. An outrush of luminous matter, resembling in
shape a partially opened fan, issued from the nucleus _towards_ the sun,
and at a certain point, like smoke driven before a high wind, was
vehemently swept backwards in a prolonged train. The appearance of the
comet at this time was compared by Bessel,[281] who watched it with
minute attention, to that of a blazing rocket. He made the singular
observation that this fan of light, which seemed the source of supply
for the tail, oscillated like a pendulum to and fro across a line
joining the sun and nucleus, in a period of 4-3/5 days; and he was
unable to escape from the conclusion[282] that a repulsive force, about
twice as powerful as the attractive force of gravity, was concerned in
the production of these remarkable effects. Nor did he hesitate to recur
to the analogy of magnetic polarity, or to declare, still more
emphatically than Olbers, "the emission of the tail to be a purely
electrical phenomenon."[283]
The transformations undergone by this body were almost as strange and
complete as those which affected the brigands in Dante's _Inferno_. When
first seen, it wore the aspect of a nebula; later it put on the
distinctive garb of a comet; it next appeared as a star; finally, it
dilated, first in a spherical, then in a paraboloidal form, until May 5,
1836, when it vanished from Herschel's observation at Feldhausen as if
by melting into adjacent space from the excessive diffusion of its
light. A very uncommon circumstance in its development was that it lost
all trace of tail _previous_ to its arrival at perihelion on the 16th of
November. Nor did it begin to recover its elongated shape for more than
two months afterwards. On the 23rd of January, Boguslawski perceived it
as a star of the sixth magnitude, _without measurable disc_.[284] Only
two nights later, Maclear, director of the Cape Observatory, found the
head to be 131 seconds across.[285] And so rapidly did the augmentation
of size progress, that Sir John Herschel estimated the actual bulk of
this singular object to have increased forty-fold in the ensuing week.
"I can hardly doubt," he remarks, "that the comet was fairly evaporated
in perihelio by the heat, and resolved into transparent vapour, and is
now in process of rapid condensation and re-precipitation on the
nucleus."[286] A plausible, but no longer admissible, interpretation of
this still unexplained phenomenon. The next return of this body, which
Public-domain text, read in full here on John Shaqi.
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