rarity, and very diaphanous.

"The luminous self-ring floated: one day it seemed to be
suspended in the diaphanous atmosphere by which the head of the
comet was surrounded, at a distance of 322,000 English miles
from the nucleus.

"This distance was not constant. The matter of the semi-annular
envelope seemed even to be precipitated by slow degrees through
the diaphanous atmosphere; finally, it reached the nucleus; the
earlier appearances vanished; the comet was reduced to a
globular nebula.

"During its period of dissolution, the ring appeared sometimes
to have several branches.

"The luminous shreds of the tail apparently underwent rapid,
frequent, and considerable variations of length. Herschel
discerned symptoms of a rotatory movement both in the comet and
its tail; a movement which carried unequal shreds from the
centre towards the border, and the border towards the centre.
On examining at intervals the same region of the tail--the
border, for example--sensible changes of length must have been
perceptible; which, however, had no reality in them. Herschel
thought that both the comet of 1811 and that of 1807 were
self-luminous. The second comet of 1811 appeared to him to
shine only by borrowed light. It must be acknowledged that
these conjectures did not rest on anything demonstrative.

"In attentively comparing the comet of 1807 with the beautiful