ever, secured by the extraordinary rapidity of its flight. It swept
past perihelion at a rate--366 miles a second--which, if continued,
would have carried it right round the sun in _two hours_; and in only
eleven minutes more than that short period it actually described half
the _curvature_ of its orbit--an arc of 180 deg.--although in travelling
over the remaining half many hundreds of sluggish years will doubtless
be consumed.

The behaviour of this comet may be regarded as an _experimentum crucis_
as to the nature of tails. For clearly no fixed appendage many millions
of miles in length could be whirled like a brandished sabre from one
side of the sun to the other in 131 minutes. Cometary trains are then,
as Olbers rightly conceived them to be, emanations, not
appendages--inconceivably rapid outflows of highly rarefied matter, the
greater part, if not all, of which becomes permanently detached from the
nucleus.

That of the comet of 1843 reached, about the time that it became visible
in this country, the extravagant length of 200 millions of miles.[292]
It was narrow, and bounded by nearly parallel and nearly rectilinear
lines, resembling--to borrow a comparison of Aristotle's--a "road"
through the constellations; and after the 3rd of March showed no trace
of hollowness, the axis being, in fact, rather brighter than the edges.
Distinctly perceptible in it were those singular aurora-like
coruscations which gave to the "tresses" of Charles V.'s comet the
appearance--as Cardan described it--of "a torch agitated by the wind,"
and have not unfrequently been observed to characterise other similar
objects. A consideration first adverted to by Olbers proves these to
originate in our own atmosphere. For owing to the great difference in
the distances from the earth of the origin and extremity of such vast
effluxes, the light proceeding from their various parts is transmitted
to our eyes in notably different intervals of time. Consequently a
luminous undulation, even though propagated instantaneously from end to
end of a comet's tail, would appear to us to occupy many minutes in its
progress. But the coruscations in question pass as swiftly as a falling
star. They are, then, of terrestrial production.

Periods of the utmost variety were by different computators assigned to
the body, which arrived at perihelion, February 27, 1843, at 9.47 p.m.
Professor Hubbard of Washington found that it required 533 years to
complete a revo