it is by the operation of those powers that the varieties of season
in spring and autumn are obtained, that we are blessed with the
vicissitudes of summer's heat and winter's cold, and that we possess the
benefit of artificial light and culinary fire.

We are thus bountifully provided with the necessaries of life; we are
supplied with things conducive to the growth and preservation of our
animal nature, and with fit subjects to employ and to nourish our
intellectual powers.

There are other actuating powers employed in the operations of this
globe, which we are little more than able to enumerate; such are those
of electricity, magnetism, and subterraneous heat or mineral fire.

Powers of such magnitude or force, are not to be supposed useless in a
machine contrived surely not without wisdom; but they are mentioned here
chiefly on account of their general effect; and it is sufficient to have
named powers, of which the actual existence is well known, but of which
the proper use in the constitution of the world is still obscure.
The laws of electricity and magnetism have been well examined by
philosophers; but the purposes of those powers in the economy of the
globe have not been discovered. Subterraneous fire, again, although the
most conspicuous in the operations of this world, and often examined by
philosophers, is a power which has been still less understood, whether
with regard to its efficient or final cause. It has hitherto appeared
more like the accident of natural things, than the inherent property of
the mineral region. It is in this last light, however, that I wish to
exhibit it, as a great power acting a material part in the operations of
the globe, and as an essential part in the constitution of this world.