it,
as a cause, those effects which are natural to it, and which, so far as
we know, cannot belong to any other. On all occasions, we are to judge
from what we know; and, we are only to avoid concluding from our
suppositions, in cases where evidence or real information is necessarily
required. The subject now considered, subterraneous fire, will afford an
example of that truth; and, a general view of this great natural power
will here find a proper place, before the application of it for the
explanation of natural appearances.

No event is more the object of our notice, or more interesting as a
subject for our study, than is the burning of a fire: But, the more that
philosophers have studied this subject, the more they seem to differ
as to the manner in which that conspicuous event is to be explained.
Therefore, being so ignorant with regard to that fire of which we see
the origin as well as the more immediate effects, how cautious should
we be in judging the nature of subterraneous fire from the burning of
bodies, a subject which we so little understand.

But, though the cause of fire in general, or the operations of that
power in its extreme degrees, be for us a subject involved in much
obscurity, this is not the case with regard to the more common effects
of heat; and, tho' the actual existence of subterraneous fire, as the
cause of light and heat, might be a thing altogether problematical in
our opinion; yet, as to other effects, there are some of these from
which the action of that liquefying power may be certainly concluded as
having taken place within the mineral region, although the cause should
be in every other respect a thing to us unknown. In that case, where the
operation or effect is evident, and cannot be disputed, to refuse to
admit the power in question, merely because we had not seen it act, or
because we know not every rule which it may observe in acting, would
be only to found an argument upon our ignorance; it would be to
misunderstand the nature of investigating physical truths, which must
proceed by reasoning from effect to cause.

Our knowledge is extremely limited with regard to the effects of heat in
bodies, while acting under different conditions, and in various degrees.
But though our knowledge in these respects is limited, our judgment with
regard to the efficacy of this power of heat is in its nature positive,
and contains not any thing that is doubtful or uncertain. All mankind,
who ha