ter and moisture of the planets, comets
(says Sir Isaac Newton) seem absolutely requisite; from whose condensed
vapours and exhalations all that moisture which is spent on vegetations
and putrefactions, and turned into dry earth, may be resupplied and
recruited; for all vegetables increase wholly from fluids, and turn by
putrefaction into earth. Hence the quantity of dry earth must continually
increase, and the moisture of the globe decrease, and at last be quite
evaporated, if it have not a continual supply. And I suspect (adds Sir
Isaac) that the spirit which makes the finest, subtilest, and best part
of our air, and which is absolutely requisite for the life and being of
all things, comes principally from the comets.

Another use which he conjectures comets may be designed to serve, is that
of recruiting the sun with fresh fuel, and repairing the consumption of
his light by the streams continually sent forth in every direction from
that luminary--

"From his huge vapouring train perhaps to shake
Reviving moisture on the numerous orbs,
Thro' which his long ellipsis winds; perhaps
To lend new fuel to declining suns,
To light up worlds, and feed th' ethereal fire."

THOMSON.

Newton has computed that the sun's heat in the comet of 1680,[2] was, to
his heat with us at Midsummer, as twenty-eight thousand to one; and that
the heat of the body of the comet was near two thousand times as great as
that of red-hot iron. The same great author also calculates, that a globe
of red-hot iron, of the dimensions of our earth, would scarce be cool in
fifty thousand years. If then the comet be supposed to cool a hundred
times as fast as red-hot iron, yet, since its heat was two thousand times
greater, supposing it of the bigness of the earth, it would not be cool
in a million of years.

An elegant writer in the Guardian, says, "I cannot forbear reflecting on
the insignificance of human art, when set in comparison with the designs
of Providence. In pursuit of this thought, I considered a comet, or in
the language of the vulgar, a blazing star, as a sky-rocket discharged by
a hand that is Almighty. Many of my readers saw that in the year 1680,
and if they were not mathematicians, will be amazed to hear, that it
travelled with a much greater degree of swiftness than a cannon ball, and
drew after it a tail of fire that was fourscore millions of miles in
length. What an amazing thought is it to consider this stupendous body