The nucleus, or head, was circular and well determined, and evidently
shone by its own light. Very small stars seemed to grow pale, "to hide
their diminished heads," when seen through its _coma_ or tail. It is
true, however, that this faintness may have been only apparent, and due
to the circumstance of the stars being projected on a luminous
background. Such was Herschel's explanation. A gaseous medium, capable
of absorbing sufficient solar radiance to efface the light of some
"lesser stars," appeared to him to possess in each stratum a sensible
quantity of matter. Hence it would cause a real diminution of the light
transmitted, though nothing would indicate the existence of such a
cause.[1]
[Footnote 1: This conclusion is disputed by many astronomers.]
Herschel examined the beautiful comet of 1811 with equal accuracy.
"Large telescopes showed him, in the midst of the gaseous head, a rather
reddish body of planetary appearance, which bore strong magnifying
powers, and showed no sign of _phase_ (that is, of change of aspect, as
in the case of the Moon).
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