o be equivalent to a greater diminution in the other.

As I could never, by means of growing vegetables, bring air which had
been thoroughly noxious to so pure a state as that a candle would burn
in it, it may be suspected that something else besides _vegetation_ is
necessary to produce this effect. But it should be considered, that no
part of the common atmosphere can ever be in this highly noxious state,
or indeed in a state in which a candle will not burn in it; but that
even air reduced to this state, either by candles actually burning out
in it, or by breathing it, has never failed to be perfectly restored by
vegetation, at least so far that candles would burn in it again, and, to
all appearance, as well, and as long as ever; so that the growing
vegetables, with which the surface of the earth is overspread, may, for
any thing that appears to the contrary, be a cause of the purification
of the atmosphere sufficiently adequate to the effect.

It may likewise be suspected, that since _agitation in water_ injures
pure common air, the agitation of the sea may do more harm than good in
this respect. But it requires a much more violent and longer continued
agitation of air in water than is ever occasioned by the waves of the
sea to do the least sensible injury to it. Indeed a light agitation of
air in _putrid water_ injures it very materially; but if the water be
sweet, this effect is not produced, except by a long and tedious
operation, whereas it requires but a very short time, in comparison, to
restore a quantity of any of the most noxious kinds of air to a very
great degree of wholesomeness by the same process.

Dr. Hales found that he could breathe the same air much longer when, in
the course of his respiration, it was made to pass through several folds
of cloth dipped in vinegar, in a solution of sea-salt, or in salt of
tartar, especially the last. Statical Essays, vol. 1. p. 266. The
experiment is valuable, and well deserves to be repeated with a greater
variety of circumstances. I imagine that the effect was produced by
those substances, or by the _water_ which they attracted from the air,
imbibing the phlogistic matter discharged from the lungs. Perhaps the
phlogiston may unite with the watery part of the atmosphere, in
preference to any other part of it, and may by that means be more easily
transferred to such salts as imbibe moisture.

Sir Isaac Newton defines _flame_ to be _fumus candens_, considering all
_