The view of the constitution of comets expounded in one of my notes
of April last, viz., that they are meteoric systems consisting of a
central mass, or masses, round which a multitude of minor bodies are
revolving like satellites around their primary, is strongly confirmed
by the curious proceedings of the present comet, which proceedings also
justify my last note of last month pointing out the omission of our
astronomers, who have neglected the positive and irregular repulsive
action of the sun upon comets, that, like the great comets of 1843,
1880, and 1882, come within a few hundred thousand miles of the visible
solar surface.
The solar prominences are stupendous eruptions from the sun,
consisting, as the spectroscope demonstrates, of hydrogen flames and
incandescent metallic vapors ejected with furious violence to visible
distances ranging from ten or twenty to above three hundred thousand
miles, but this flame shown by the spectroscope is but the flash of
the gun, the actual ejection proceeding vastly farther, far beyond
the limits of the corona, as described in last month’s notes. These
eruptions are so abundant that Secchi alone observed and recorded 2767
in one year (1871). Speaking generally, the sun is never free from
them, and they proceed from all parts of the sun, but most abundantly
from the sun-spot zones.
A system of meteoric bodies such as I suppose to form a comet (I mean
the comet as it exists in space before the generation of its tail,
which is only formed as it approaches the sun) could not approach
so near to the sun as did the present comet at perihelion, without
encountering more or less of these furious blasts the flash of some of
which have been seen to move with a measurable mean velocity of above
300 miles per second, and a probable maximum velocity sufficient to
eject solid matter beyond the reclaiming grasp of solar gravitation.
It is evident that such a meteoric system as I suppose to constitute
a comet would, in the course of a rapid perihelion flight crossing
these outblasts, be liable to various degrees of ejection in different
parts, that would disturb its original structure by blowing some of its
constituents out of their orbits, or even quite away from the control
of the feeble gravitation of the general meteoric mass, and thus
effecting a rupture of the comet.
Now such a disintegration or dispersion of the present comet has been
actually observed. Several able observers have described a breaking of
the head of this comet shortly after its perihelion passage. Commander
Sampson’s observations with the great 26-inch equatorial telescope of
the Washington Naval Observatory are very explicit. On October 25 he
saw the nucleus as a single well-defined globular body. On November 3,
with the same telescope, he saw a triple nucleus, due to the formation
of two additional minor bodies. These were more distinctly seen on
November 6. Mr. W. R. Brooks, of New York, saw a detached fragment
of the comet which afterwards faded out of view. Professor Schmidt
observed another and similar fragment which has likewise disappeared.
All these observations indicate disruption due to some disturbing
force, acting with different degrees of violence upon different
portions of the comet.
Minor disturbances of this kind will, I think, account for the trail
of meteoric bodies which Schiaparelli has shown to follow the paths of
other comets. A great disturbance might give quite a new orbit to the
meteoric fragments.
These considerations suggest another and a curious view of the question
of possible cometary collision with the sun, viz., that a comet might
be traveling in such an orbit as to make it mathematically due to
plunge obliquely beneath the solar surface at its next perihelion; but
on its approach to the surface of the sun it might encounter so violent
an outrush of solar-prominence matter as to drive it bodily out of its
course, and avert the threatened peril to its existence.