nature of the earth, and of all the bodies that are most generally
found upon it, as air, water, fire, the loadstone and other
minerals. In the next place it is necessary also to examine singly
the nature of plants, of animals, and above all of man, in order
that we may thereafter be able to discover the other sciences that
are useful to us. Thus, all Philosophy is like a tree, of which
Metaphysics is the root, Physics the trunk, and all the other
sciences the branches that grow out of this trunk, which are reduced
to three principal, namely, Medicine, Mechanics, and Ethics. By the
science of Morals, I understand the highest and most perfect which,
presupposing an entire knowledge of the other sciences, is the last
degree of wisdom.

But as it is not from the roots or the trunks of trees that we
gather the fruit, but only from the extremities of their branches,
so the principal utility of philosophy depends on the separate uses
of its parts, which we can only learn last of all. But, though I am
ignorant of almost all these, the zeal I have always felt in
endeavouring to be of service to the public, was the reason why I
published, some ten or twelve years ago, certain Essays on the
doctrines I thought I had acquired. The first part of these Essays
was a "Discourse on the Method of rightly conducting the Reason, and
seeking Truth in the Sciences," in which I gave a summary of the
principal rules of logic, and also of an imperfect ethic, which a
person may follow provisionally so long as he does not know any
better. The other parts were three treatises: the first of
Dioptrics, the second of Meteors, and the third of Geometry. In the
Dioptrics, I designed to show that we might proceed far enough in
philosophy as to arrive, by its means, at the knowledge of the arts
that are useful to life, because the invention of the telescope, of