, 27), "Cometes aternos esse et
sortis ejusdem, cujus caetera (sidera), etiamsi faciem illis non habent
similem." Pliny (ii., 25) also refers to Apollonius Myndius, when he says,
"Sunt qui et haec sidera perpetua esse credant suoque ambitu ire, sed non
nisi relicta a sole cerni."
p 104
The occulation of the fixed stars by the nucleus of a comet, or by its
innermost vaporous envelopes, might throw some light on the physical
character of these wonderful bodies; but we are unfortunately deficient in
observations by which we may be assured* that the occulation was perfectly
central; for, as it has already been observed, the parts of the envelope
contiguous to the nucleus are alternately composed of layers of dense or
very attenuated vapor.
[footnote] *Olbers, in 'Astr. Nachr.', 1828, s. 157, 184. Arago, 'De la
Constitution physique des Cometes; Annuaire de' 1832, p. 203, 208. The
ancients were struck by the phenomenon that it was possible to see through
comets as through a flame. The earliest evidence to be met with of stars
having been seen through comets is that of Democritus (Aristot., 'Meteor.',
i., 6, 11), and the statement leads Aristotle to make the not unimportant
remark, that he himself had observed the occulation of one of the stars of
Gemini by Jupiter.
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