nd scrutiny. We may here, as it were, seize nature in the
act, and trace out the actual progress of developments which at present
are matters rather of theory than of observation.

VIII.

_COMETS AS PORTENTS_

The blazing star,
Threat'ning the world with famine, plague, and war;
To princes death; to kingdoms many curses;
To all estates inevitable losses;
To herdsmen rot; to ploughmen hapless seasons;
To sailors storms; to cities civil treasons.

Although comets are no longer regarded with superstitious awe as in old
times, mystery still clings to them. Astronomers can tell what path a
comet is travelling upon, and say whence it has come and whither it will
go, can even in many cases predict the periodic returns of a comet, can
analyse the substance of these strange wanderers, and have recently
discovered a singular bond of relationship between comets and those
other strange visitants from the celestial depths, the shooting stars.
But astronomy has hitherto proved unable to determine the origin of
comets, the part they perform in the economy of the universe, their real
structure, the causes of the marvellous changes of shape which they
undergo as they approach the sun, rush round him, and then retreat. As
Sir John Herschel has remarked: 'No one, hitherto, has been able to
assign any single point in which we should be a bit better or worse off,
materially speaking, if there were no such thing as a comet. Persons,
even thinking persons, have busied themselves with conjectures; such as
that they may serve for fuel for the sun (into which, however, they
never fall), or that they may cause warm summers, which is a mere fancy,
or that they may give rise to epidemics, or potato-blights, and so
forth.' And though, as he justly says, 'this is all wild talking,' yet
it will probably continue until astronomers have been able to master the
problems respecting comets which hitherto have foiled their best
efforts. The unexplained has ever been and will ever be marvellous to
the general mind. Just as unexplored regions of the earth have been
tenanted in imagination by

anthropophagi and men whose heads
Do grow beneath their shoulders,

so do wondrous possibilities exist in the unknown and the ill-understood
phenomena of nature.

In old times, when the appearance and movements of comets were supposed
to be altogether uncontrolled by physical laws, it was natural that
comet