The truth is, the Science of Nature has been already too long made only a work of the _Brain_ and the _Fancy_: It is now high time that it should return to the plainness and soundness of _Observations_ on _material_ and _obvious_ things. It is said of great Empires, That _the best way to preserve them from decay, is to bring them back to the first Principles, and Arts, on which they did begin_. The same is undoubtedly true in Philosophy, that by wandring far away into _invisible Notions_, has almost quite destroy’d it self, and it can never be recovered, or continued, but by returning into the same _sensible paths_, in which it did at first proceed. If therefore the Reader expects from me any infallible Deductions, or certainty of _Axioms_, I am to say for my self, that those stronger Works of Wit and Imagination are above my weak Abilities; or if they had not been so, I would not have made use of them in this present Subject before me: Whenever he finds that I have ventur’d at any small Conjectures, at the causes of the things that I have observed, I beseech him to look upon them only as _doubtful Problems_, and _uncertain ghesses_, and not as unquestionable Conclusions, or matters of unconfutable Science; I have produced nothing here, with intent to bind his understanding to an _implicit_ consent; I am so far from that, that I desire him, not absolutely to rely upon these Observations of my eyes, if he finds them contradicted by the future Ocular Experiments of sober and impartial Discoverers. As for my part, I have obtained my end, if these my small Labours shall be thought fit to take up some place in the large stock of _natural Observations_, which so many hands are busie in providing. If I have contributed the _meanest foundations_ whereon others may raise nobler _Superstructures_, I am abundantly satisfied; and all my ambition is, that I may serve to the great Philosophers of this Age, as the makers and the grinders of my Glasses did to me; that I may prepare and furnish them with some _Materials_, which they may afterwards _order_ and _manage_ with better skill, and to far greater advantage. The next remedies in this universal cure of the Mind are to be applied to the _Memory_, and they are to consist of such Directions as may inform us, what things are best to be _stor’d up_ for our purpose, and which is the best way of so _disposing_ them, that they may not only be _kept in safety_, but ready and convenient, to be at any time _produc’d_ for use, as occasion shall require. But I will not here prevent my self in what I may say in another Discourse, wherein I shall make an attempt to propose some Considerations of the manner of compiling a Natural and Artificial History, and of so ranging and registring its Particulars into Philosophical Tables, as may make them most useful for the raising of _Axioms_ and _Theories_.