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
comet of 1811, relative to the changes of distance from the
Sun, and the modifications resulting thence, Herschel put it
beyond doubt that these modifications have something individual
in them,--something relative to a special state of the nebulous
matter. On one celestial body the changes of distance produce
an enormous effect, on another the modifications are
insignificant."
We have reproduced these observations by a distinguished French
astronomer, in order to show the reader what was the nature, and how
great was the importance, of Herschel's labours, and in how remarkable
and comprehensive a manner he conducted his survey of the celestial
phenomena.
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