already ascribed to the fifth year of
Justinian, which coincides with the five hundred and thirty-first of
the Christian aera. And it may deserve notice, that in this, as in the
preceding instance, the comet was followed, though at a longer interval,
by a remarkable paleness of the sun. The _sixth_ return, in the year
eleven hundred and six, is recorded by the chronicles of Europe and
China: and in the first fervor of the crusades, the Christians and
the Mahometans might surmise, with equal reason, that it portended the
destruction of the Infidels. The _seventh_ phenomenon, of one thousand
six hundred and eighty, was presented to the eyes of an enlightened age.
The philosophy of Bayle dispelled a prejudice which Milton's muse had
so recently adorned, that the comet, "from its horrid hair shakes
pestilence and war." Its road in the heavens was observed with exquisite
skill by Flamstead and Cassini: and the mathematical science of
Bernoulli, Newton, and Halley, investigated the laws of its
revolutions. At the _eighth_ period, in the year two thousand three
hundred and fifty-five, their calculations may perhaps be verified
by the astronomers of some future capital in the Siberian or American
wilderness.

II. The near approach of a comet may injure or destroy the globe which
we inhabit; but the changes on its surface have been hitherto produced
by the action of volcanoes and earthquakes. The nature of the soil may
indicate the countries most exposed to these formidable concussions,
since they are caused by subterraneous fires, and such fires are kindled
by the union and fermentation of iron and sulphur. But their times
and effects appear to lie beyond the reach of human curiosity; and the
philosopher will discreetly abstain from the prediction of earthquakes,
till he has counted the drops of water that silently filtrate on
the inflammable mineral, and measured the caverns which increase by
resistance the explosion of the imprisoned air. Without assigning the
cause, history will distinguish the periods in which these calamitous
events have been rare or frequent, and will observe, that this fever of
the earth raged with uncommon violence during the reign of Justinian.
Each year is marked by the repetition of earthquakes, of such duration,
that Constantinople has been shaken above forty days; of such extent,
that the shock has been communicated to the whole surface of the globe,
or at least of the Roman empire. An impulsive or