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to finding the composition of the heavenly
bodies, there was a great desire to find out
what comets are made of. The first oppor-
tunity came in 1864, when Donati observed
the spectrum of a comet, and saw three
bright bands, thus proving that it was a gas
and at least partly self-luminous. In 1868
Huggins compared the spectrum of Win-
necke’s comet with that of a Geissler tube
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