ation of the earth, as well as in its
annual revolution. In this manner are produced the vicissitudes of night
and day, so variable in the different latitudes from the equator to the
pole, and so beautifully calculated to equalise the benefits of light,
so variously distributed in the different regions of the globe.

Gravitation, and the _vis infita_ of matter, thus form the first two
powers distinguishable in the operations of our system, and wisely
adapted to the purpose for which they are employed.

We next observe the influence of light and heat, of cold and
condensation. It is by means of these two powers that the various
operations of this living world are more immediately transacted;
although the other powers are no less required, in order to produce or
modify these great agents in the economy of life, and system of our
changing things.

We do not now inquire into the nature of those powers, or investigate
the laws of light and heat, of cold and condemnation, by which the
various purposes of this world are accomplished; we are only to mention
those effects which are made sensible to the common understanding of
mankind, and which necessarily imply a power that is employed. Thus,
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