which I there gave an explanation, is one of the most difficult that
has ever been made. In the treatise of Meteors, I desired to exhibit
the difference that subsists between the philosophy I cultivate and
that taught in the schools, in which the same matters are usually
discussed. In fine, in the Geometry, I professed to demonstrate that
I had discovered many things that were before unknown, and thus
afford ground for believing that we may still discover many others,
with the view of thus stimulating all to the investigation of truth.
Since that period, anticipating the difficulty which many would
experience in apprehending the foundations of the Metaphysics, I
endeavoured to explain the chief points of them in a book of
Meditations, which is not in itself large, but the size of which has
been increased, and the matter greatly illustrated, by the
Objections which several very learned persons sent to me on occasion
of it, and by the Replies which I made to them. At length, after it
appeared to me that those preceding treatises had sufficiently
prepared the minds of my readers for the Principles of Philosophy, I
also published it; and I have divided this work into four parts, the
first of which contains the principles of human knowledge, and which
may be called the First Philosophy, or Metaphysics. That this part,
accordingly, may be properly understood, it will be necessary to
read beforehand the book of Meditations I wrote on the same subject.
The other three parts contain all that is most general in Physics,
namely, the explication of the first laws or principles of nature,
and the way in which the heavens, the fixed stars, the planets,
comets, and generally the whole universe, were composed; in the next
place, the explication, in particular, of the nature of this earth,
the air, water, fire, the magnet, which are the bodies we most
commonly find everywhere around it, and of all the qualities we
observe in these bodies, as light, heat, gravity, and the like. In