ghtness, since there is a manifest waste of their material at each
near approach to the sun; until at length the comet is seen no more, not
because it has left the warm precincts of the sun for the outer
darkness, but because it has spent its substance. Halley's comet was not
as brilliant or as impressive in 1835 as it was in 1759: in 1910 it may
have become degraded to an appearance of quite the second order.

Next, we have no knowledge, no evidence, that any of these comets have
always been members of the solar family. Some of them, indeed, we know
were adopted into it by the influence of one or other of the greater
planets: Uranus we know is responsible for the introduction of one,
Jupiter of a considerable number. The vast majority of comets, great or
small, seem to blunder into the solar system anyhow, anywhere, from any
direction: they come within the attractive influence of the sun; obey
his laws whilst within that influence; make one close approach to him,
passing rapidly across our sky; and then depart in an orbit which will
never bring them to his neighbourhood again. Some chance of direction,
some compelling influence of a planet that it may have approached, so
modified the path of Halley's comet when it first entered the solar
system, that it has remained a member ever since, and may so remain
until it has ceased to be a comet at all.

It follows, therefore, that, as to the number of great comets that may
be seen in any age, we can scarcely even apply the laws of probability.
During the last couple of thousand years, since chronicles have been
abundant, we know that many great comets have been seen. We may suppose,
therefore, that during the preceding age, that in which the Scriptures
were written, there were also many great comets seen, but we do not
know. And most emphatically we are not able to say, from our knowledge
of comets themselves and of their motions, that in the days of this or
that writer a comet was flaming in the sky.

If a comet had been observed in those ages we might not recognize the
description of it. Thus in the fourth year of the 101st Olympiad, the
Greeks were startled by a celestial portent. They did not draw fine
distinctions, and posterity might have remained ignorant that the
terrifying object was possibly a comet, had not Aristotle, who saw it as
a boy at Stagira, left a rather more scientifically worded description
of it. It flared up from the sunset sky with a narrow definite