heated body. This necessity of heating any body we mean to
burn depends upon certain considerations, which have not hitherto been
attended to by any natural philosopher, for which reason I shall enlarge
a little upon the subject in this place.

Nature is at present in a state of equilibrium, which cannot have been
attained until all the spontaneous combustions or oxygenations possible
in the ordinary degrees of temperature had taken place. Hence, no new
combustions or oxygenations can happen without destroying this
equilibrium, and raising the combustible substances to a superior degree
of temperature. To illustrate this abstract view of the matter by
example: Let us suppose the usual temperature of the earth a little
changed, and that it is raised only to the degree of boiling water; it
is evident, that, in this case, phosphorus, which is combustible in a
considerably lower degree of temperature, would no longer exist in
nature in its pure and simple state, but would always be procured in its
acid or oxygenated state, and its radical would become one of the
substances unknown to chemistry. By gradually increasing the
temperature of the earth the same circumstance would successively happen
to all the bodies capable of combustion; and, at last, every possible
combustion having taken place, there would no longer exist any
combustible body whatever, as every substance susceptible of that
operation would be oxygenated, and consequently incombustible.

There cannot therefore exist, so far as relates to us, any combustible
body, except such as are incombustible in the ordinary temperatures of
the earth; or, what is the same thing, in other words, that it is
essential to the nature of every combustible body not to possess the
property of combustion, unless heated, or raised to the degree of
temperature at which its combustion naturally takes place. When this
degree is once produced, combustion commences, and the caloric which is
disengaged by the decomposition of the oxygen gas keeps up the
temperature necessary for continuing combustion. When this is not the
case, that is, when the disengaged caloric is insufficient for keeping
up the necessary temperature, the combustion ceases: This circumstance
is expressed in common language by saying, that a body burns ill, or
with difficulty.

Although combustion possesses some circumstances in common with
distillation, especially with the compound kind of that operation, they
diffe