Philosophical Letters: OR, MODEST REFLECTIONS Upon some Opinions in _NATURAL PHILOSOPHY_, MAINTAINED By several Famous and Learned Authors of this Age, Expressed by way of LETTERS: By the Thrice Noble, Illustrious, and Excellent Princess, The Lady MARCHIONESS of _NEWCASTLE_. _LONDON_, Printed in the Year, 1664. TO HER EXCELLENCY The Lady Marchioness of NEWCASTLE On her Book of Philosophical Letters. _'Tis Supernatural, nay 'tis Divine, To write whole Volumes ere I can a line. I 'mplor'd the Lady Muses, those fine things, But they have broken all their Fidle-strings And cannot help me; Nay, then I did try Their_ Helicon, _but that is grown all dry:_ _Then on_ Parnassus _I did make a sallie, But that's laid level, like a Bowling-alley; Invok'd my Muse, found it a Pond, a Dream, To your eternal Spring, and running Stream; So clear and fresh, with Wit and Phansie store, As then despair did bid me write no more._ W. Newcastle. TO HIS EXCELLENCY The Lord Marquis of NEWCASTLE. My Noble Lord, Although you have, always encouraged me in my harmless pastime of Writing, yet was I afraid that your Lordship would be angry with me for Writing and Publishing this Book, by reason it is a Book of Controversies, of which I have heard your Lordship say, That Controversies and Disputations make Enemies of Friends, and that such Disputations and Controversies as these, are a pedantical kind of quarrelling, not becoming Noble Persons. But your Lordship will be pleased to consider in my behalf, that it is impossible for one Person to be of every one's Opinion, if their opinions be different, and that my Opinions in Philosophy, being new, and never thought of, at least not divulged by any, but my self, are quite different from others: For the Ground of my Opinions is, that there is not onely a Sensitive, but also a Rational Life and Knowledge, and so a double Perception in all Creatures: And thus my opinions being new, are not so easily understood as those, that take up several pieces of old opinions, of which they patch up a new Philosophy, (if new may be made of old things,) like a Suit made up of old Stuff bought at the Brokers: Wherefore to find out a Truth, at least a Probability in Natural Philosophy by a new and different way from other Writers, and to make this way more known, easie and intelligible, I was in a manner forced to write this Book; for I have not contradicted those Authors in any thing, but what concerns and is opposite to my opinions; neither do I anything, but what they have done themselves, as being common amongst them to contradict each other: which may as well be allowable, as for Lawyers to plead at the Barr in opposite Causes. For as Lawyers are not Enemies to each other, but great Friends, all agreeing from the Barr, although not at the Barr: so it is with Philosophers, who make their Opinions as their Clients, not for Wealth, but for Fame, and therefore have no