The _equated isocrone Motion_ of the weight of a _Circular Pendulum_ in a _Paraboloid_, for the regulating of _Clocks_; and the improving _Pocket-Watches_ by _Springs_ applied to the _Ballance_, were first invented and demonstrated to this Society by Dr. _Hooke_; together with all those _New_ and useful _Instruments_, _Contrivances_ and _Experiments_, _Mathematical_ and _Physical_, publish’d in his _Posthumous Works_ by the most accomplish’d Mr. _Waller_, _Secretary_ to the _R. Society_. And since those the incomparably learned Sir _Isaac Newton_, now _President_ of the _Royal Society_; Mr. _Haly_, the Worthy _Professor_ of _Geometry_ in the _University_ of _Oxford_; Dr. _Grew_, and several more, whose Works and useful Inventions sufficiently celebrate their Merits: I did mention the _Barometer_, to which might be added the prodigious effects of the _Speculum Ustorium_, surpassing what the _French_ pretend to, as confidently, or rather _audaciously_, they do, and to other admirable Inventions, injuriously _arrogated_ by _Strangers_, tho’ due of right to _Englishmen_, and Members of this Society; but ’tis not the business of this Preface to enumerate all, tho’ ’twas necessary to touch on some Instances. {xciii:1} Neh. 2. 19. {xciii:2} Neh. 4. 17. {xcvi:1} _Since this _Epistle_ was first written and publish’d the _University of Oxford_ have instituted, and erected a _Society_ for the promoting of _Natural_ and _Experimental Knowledge_, in consort with the _R. Society_, with which they keep a mutual Correspondence: This mention, for that some _Malevolents_ had so far endeavour’d to possess divers Members of the _University_; as if the _Society_ design’d nothing less than the undermining of that, and other illustrious _Academies_, and which indeed so far prevail’d, as to breed a real Jealousy for some considerable time: But as this was never in the Thoughts of the _Society_ (which had ever the _Universities_ in greatest Veneration) so the Innocency and Usefulness of its Institution has at length disabus’d them, vindicated their Proceedings, dissipated all Surmises, and, in fine, produced an ingenious, friendly and candid Union and Correspondence between them._ ADVERTISEMENT.