y students of science
would remain, after the catastrophe, to estimate or to record its
effects.

Fortunately, all that we have learned hitherto from the stars favours
the belief that, while a catastrophe of this sort may be possible, it is
exceedingly unlikely. We may estimate the probabilities precisely in the
same way that an insurance company estimates the chance of a railway
accident. Such a company considers the number of accidents which occur
among a given number of railway journeys, and from the smallness of the
number of accidents compared with the largeness of the number of
journeys estimates the safety of railway travelling. Our sun is one
among many millions of suns, any one of which (though all but a few
thousands are actually invisible) would become visible to the naked eye,
if exposed to the same conditions as have affected the suns in flames
described in the preceding pages. Seeing, then, that during the last
two thousand years or thereabouts, only a few instances of the kind,
certainly not so many as twenty, have been recorded, while there is
reason to believe that some of these relate to the same star which has
blazed out more than once, we may fairly consider the chance exceedingly
small that during the next two thousand, or even the next twenty
thousand years, our sun will be exposed to a catastrophe of the kind.

We might arrive at this conclusion independently of any considerations
tending to show that our sun belongs to a safe class of system-rulers,
and that all, or nearly all, the great solar catastrophes have occurred
among suns of a particular class. There are, however, several
considerations of the kind which are worth noting.

In the first place, we may dismiss as altogether unlikely the visit of a
comet from the star-depths to our sun, on a course carrying the comet
directly upon the sun's surface. But if, among the comets travelling in
regular attendance upon the sun, there be one whose orbit intersects the
sun's globe, then that comet must several times ere this have struck the
sun, raising him temporarily to a destructive degree of heat. Now, such
a comet must have a period of enormous length, for the races of animals
now existing upon the earth must all have been formed since that comet's
last visit--on the assumption, be it remembered, that the fall of a
large comet upon the sun, or rather the direct passage of the sun
through the meteoric nucleus of a large comet, would excite the s