Some of the most conspicuous of these luminous
developments occurred on October 11th, when the comet was at its
nearest approach to the earth, and on
{p. 66}
October 17th, when it was nearest to the planet Venus. He has no
doubt that the close neighborhood of the earth and Venus at those
times was the effective cause of the sudden changes of aspect, and
that those changes of aspect may be accepted _as proof that the
comet's substance consists of "really ponderable material."_
Mr. Lockyer used the spectroscope to analyze the light of Coggia's
comet, and he established beyond question that--
"Some of the rays of the comet were sent either from _solid
particles_, or from vapor in a state of _very high condensation_, and
also that beyond doubt other portions of the comet's light issue from
the vapor _shining by its own inherent light_. The light coming from
the more dense constituents, and therefore giving a continuous
colored spectrum, was, however, deficient in blue rays, and was most
probably emitted _by material substance at the low red and yellow
stages of incandescence_.
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