Method of Composition. This Analysis consists in making Experiments and
Observations, and in drawing general Conclusions from them by Induction,
and admitting of no Objections against the Conclusions, but such as are
taken from Experiments, or other certain Truths. For Hypotheses are not
to be regarded in experimental Philosophy. And although the arguing from
Experiments and Observations by Induction be no Demonstration of general
Conclusions; yet it is the best way of arguing which the Nature of
Things admits of, and may be looked upon as so much the stronger, by how
much the Induction is more general. And if no Exception occur from
Ph nomena, the Conclusion may be pronounced generally. But if at any
time afterwards any Exception shall occur from Experiments, it may then
begin to be pronounced with such Exceptions as occur. By this way of
Analysis we may proceed from Compounds to Ingredients, and from Motions
to the Forces producing them; and in general, from Effects to their
Causes, and from particular Causes to more general ones, till the
Argument end in the most general. This is the Method of Analysis: And
the Synthesis consists in assuming the Causes discover'd, and
establish'd as Principles, and by them explaining the Ph nomena
proceeding from them, and proving the Explanations.
In the two first Books of these Opticks, I proceeded by this Analysis to
discover and prove the original Differences of the Rays of Light in
respect of Refrangibility, Reflexibility, and Colour, and their
alternate Fits of easy Reflexion and easy Transmission, and the
Properties of Bodies, both opake and pellucid, on which their Reflexions
and Colours depend. And these Discoveries being proved, may be assumed
in the Method of Composition for explaining the Ph nomena arising from
them: An Instance of which Method I gave in the End of the first Book.
In this third Book I have only begun the Analysis of what remains to be
discover'd about Light and its Effects upon the Frame of Nature, hinting
several things about it, and leaving the Hints to be examin'd and
improv'd by the farther Experiments and Observations of such as are
inquisitive. And if natural Philosophy in all its Parts, by pursuing
this Method, shall at length be perfected, the Bounds of Moral
Philosophy will be also enlarged. For so far as we can know by natural
Philosophy what is the first Cause, what Power he has over us, and what
Benefits we receive from him, so far our Duty towards him, as well as
that towards one another, will appear to us by the Light of Nature. And
no doubt, if the Worship of false Gods had not blinded the Heathen,
their moral Philosophy would have gone farther than to the four
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