ed, however, that the
spectroscope has rather increased than diminished the mystery which, in
some respects, surrounds the constitution of these bodies. The older
astronomy has satisfactorily accounted for their appearance, and we
might also say for their origin and their end, so far as questions of
origin can come into the domain of science. It is now known that comets
are not wanderers through the celestial spaces from star to star, but
must always have belonged to our system. But their orbits are so very
elongated that thousands, or even hundreds of thousands, of years are
required for a revolution. Sometimes, however, a comet passing near to
Jupiter is so fascinated by that planet that, in its vain attempts to
follow it, it loses so much of its primitive velocity as to circulate
around the sun in a period of a few years, and thus to become,
apparently, a new member of our system. If the orbit of such a comet,
or in fact of any comet, chances to intersect that of the earth, the
latter in passing the point of intersection encounters minute particles
which cause a meteoric shower.

But all this does not tell us much about the nature and make-up of a
comet. Does it consist of nothing but isolated particles, or is there a
solid nucleus, the attraction of which tends to keep the mass together?
No one yet knows. The spectroscope, if we interpret its indications in
the usual way, tells us that a comet is simply a mass of hydrocarbon
vapor, shining by its own light. But there must be something wrong in
this interpretation. That the light is reflected sunlight seems to
follow necessarily from the increased brilliancy of the comet as it
approaches the sun and its disappearance as it passes away.

Great attention has recently been bestowed upon the physical
constitution of the planets and the changes which the surfaces of those
bodies may undergo. In this department of research we must feel
gratified by the energy of our countrymen who have entered upon it.
Should I seek to even mention all the results thus made known I might
be stepping on dangerous ground, as many questions are still unsettled.
While every astronomer has entertained the highest admiration for the
energy and enthusiasm shown by Mr. Percival Lowell in founding an
observatory in regions where the planets can be studied under the most
favorable conditions, they cannot lose sight of the fact that the
ablest and most experienced observers are liable to error when