of comets is "exhalation," and says, "If this exhalation is thick
and sticky, it blazes into a comet." And again he returns to the
same view, saying that "one form of exhalation is dense, hence easily
inflammable and long retentive of fire, from which sort are especially
generated comets." But it is in his third lecture that he takes up
comets specially, and his discussion of them is extended through the
fourth, fifth, and sixth lectures. Having given in detail the opinions
of various theologians and philosophers, he declares his own in the form
of two conclusions. The first of these is that "comets are not heavenly
bodies, but originate in the earth's atmosphere below the moon; for
everything heavenly is eternal and incorruptible, but comets have a
beginning and ending--ergo, comets can not be heavenly bodies." This,
we may observe, is levelled at the observations and reasonings of Tycho
Brahe and Kepler, and is a very good illustration of the scholastic
and mediaeval method--the method which blots out an ascertained fact by
means of a metaphysical formula. His second conclusion is that "comets
are of elemental and sublunary nature; for they are an exhalation
hot and dry, fatty and well condensed, inflammable and kindled in
the uppermost regions of the air." He then goes on to answer sundry
objections to this mixture of metaphysics and science, and among other
things declares that "the fatty, sticky material of a comet may be
kindled from sparks falling from fiery heavenly bodies or from a
thunderbolt"; and, again, that the thick, fatty, sticky quality of the
comet holds its tail in shape, and that, so far are comets from having
their paths beyond the moon's orbit, as Tycho Brahe and Kepler thought,
he himself in 1618 saw "a bearded comet so near the summit of Vesuvius
that it almost seemed to touch it." As to sorts and qualities of
comets, he accepts Aristotle's view, and divides them into bearded and
tailed.(106) He goes on into long disquisitions upon their colours,
forms, and motions. Under this latter head he again plunges deep into
a sea of metaphysical considerations, and does not reappear until he
brings up his compromise in the opinion that their movement is as yet
uncertain and not understood, but that, if we must account definitely
for it, we must say that it is effected by angels especially assigned to
this service by Divine Providence. But, while proposing this compromise
between science and theology as to