produce as great a certitude as those of Geometry, and which even
differ much therefrom, since whereas the Geometers prove their
Propositions by fixed and incontestable Principles, here the
Principles are verified by the conclusions to be drawn from them; the
nature of these things not allowing of this being done otherwise.
It is always possible to attain thereby to a degree of probability
which very often is scarcely less than complete proof. To wit, when
things which have been demonstrated by the Principles that have been
assumed correspond perfectly to the phenomena which experiment has
brought under observation; especially when there are a great number of
them, and further, principally, when one can imagine and foresee new
phenomena which ought to follow from the hypotheses which one employs,
and when one finds that therein the fact corresponds to our prevision.
But if all these proofs of probability are met with in that which I
propose to discuss, as it seems to me they are, this ought to be a
very strong confirmation of the success of my inquiry; and it must be
ill if the facts are not pretty much as I represent them. I would
believe then that those who love to know the Causes of things and who
are able to admire the marvels of Light, will find some satisfaction
in these various speculations regarding it, and in the new explanation
of its famous property which is the main foundation of the
construction of our eyes and of those great inventions which extend so
vastly the use of them.
I hope also that there will be some who by following these beginnings
will penetrate much further into this question than I have been able
to do, since the subject must be far from being exhausted. This
appears from the passages which I have indicated where I leave certain
difficulties without having resolved them, and still more from matters
which I have not touched at all, such as Luminous Bodies of several
sorts, and all that concerns Colours; in which no one until now can
boast of having succeeded. Finally, there remains much more to be
investigated touching the nature of Light which I do not pretend to
have disclosed, and I shall owe much in return to him who shall be
able to supplement that which is here lacking to me in knowledge. The
Hague. The 8 January 1690.
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