un to
destructive heat. If all living creatures on the earth are to be
destroyed when some comet belonging to the solar system makes its next
return to the sun, that same comet at its last visit must have raised
the sun to an equal, or even greater intensity of heat, so that either
no such races as at present exist had then come into being, or, if any
such existed, they must at that time have been utterly destroyed. We
may fairly believe that all comets of the destructive sort have been
eliminated. Judging from the evidence we have on the subject, the
process of the formation of the solar system was one which involved the
utilisation of cometic and meteoric matter; and it fortunately so
chanced that the comets likely otherwise to have been most
mischievous--those, namely, which crossed the track of planets, and
still more those whose paths intersected the globe of the sun--were
precisely those which would be earliest and most thoroughly used up in
this way.

Secondly, it is noteworthy that all the stars which have blazed out
suddenly, except one, have appeared in a particular region of the
heavens--the zone of the Milky Way (all, too, on one half of that zone).
The single exception is the star in the Northern Crown, and that star
appeared in a region which I have found to be connected with the Milky
Way by a well-marked stream of stars, not a stream of a few stars
scattered here and there, but a stream where thousands of stars are
closely aggregated together, though not quite so closely as to form a
visible extension of the Milky Way. In my map of 324,000 stars this
stream can be quite clearly recognised; but, indeed, the brighter stars
scattered along it form a stream recognisable with the naked eye, and
have long since been regarded by astronomers as such, forming the stars
of the Serpent and the Crown, or a serpentine streak followed by a loop
of stars shaped like a coronet. Now the Milky Way, and the outlying
streams of stars connected with it, seem to form a region of the stellar
universe where fashioning processes are still at work. As Sir W.
Herschel long since pointed out, we can recognise in various parts of
the heavens various stages of development, and chief among the regions
where as yet Nature's work seems incomplete, is the Galactic
zone--especially that half of it where the Milky Way consists of
irregular streams and clouds of stellar light. As there is no reason for
believing that our sun belongs to thi