comet of 1882 was in any case a distinct body, it
seems more likely that we have here a family of comets approaching the
sun from the same region of space and pursuing almost the same course.
We know a few other instances of such resemblances between the orbits of
distinct comets.

Of other interesting comets seen within the last few years we may
mention one discovered by Mr. Holmes in London on the 6th November,
1892. It was then situated not far from the bright nebula in the
constellation Andromeda, and like it was just visible to the naked eye.
The comet became gradually fainter and more diffused, but on the 16th
January following it appeared suddenly with a central condensation, like
a star of the eighth magnitude, surrounded by a small coma. Gradually it
expanded again, and grew fainter, until it was last observed on the 6th
April.[32] The orbit was found to be an ellipse more nearly circular
than the orbit of any other known comet, the period being nearly seven
years. Another comet of 1892 is remarkable as having been discovered by
Professor Barnard, of the Lick Observatory, on a photograph of a region
in Aquila; he was at once able to distinguish the comet from a nebula by
its motion.

Since 1864 the light of every comet which has made its appearance has
been analysed by the spectroscope. The slight surface-brightness of
these bodies renders it necessary to open the slit of the spectroscope
rather wide, and the dispersion employed cannot be very great, which
again makes accurate measurements difficult. The spectrum of a comet is
chiefly characterised by three bright bands shading gradually off
towards the violet, and sharply defined on the side towards the red.
This appearance is caused by a large number of fine and close lines,
whose intensity and distance apart decrease towards the violet. These
three bands reveal the existence of hydrocarbon in comets.

The important _role_ which we thus find carbon playing in the
constitution of comets is especially striking when we reflect on the
significance of the same element on the earth. We see it as the chief
constituent of all vegetable life, we find it to be invariably present
in animal life. It is an interesting fact that this element, of such
transcendent importance on the earth, should now have been proved to be
present in these wandering bodies. The hydrocarbon bands are, however,
not always the only features visible in cometary spectra. In a comet
seen in th