Here is presented to thy view one of the Abstrusest as well as the Gentilest Subjects of Natural Philosophy, the _Experimentall History of Colours_; which though the Noble Author be pleased to think but _Begun_, yet I must take leave to say, that I think it so well begun, that the work is more than half dispatcht. Concerning which I cannot but give this advertisement to the Reader, that I have heard the Author express himself, that it would not surprise him, if it should happen to be objected, that some of these Experiments have been already published, partly by Chymists, and partly by two or three very fresh Writers upon other Subjects. And though the number of these Experiments be but very small, and though they be none of the considerablest, yet it may on this occasion be further represented, that it is easie for our Author to name several men, (of whose number I can truly name my self) who remember either their having seen him make, or their having read, his Accounts of the Experiments delivered in the following Tract several years since, and long before the publication of the Books, wherein they are mentioned. Nay in divers passages (where he could do it without any great inconvenience) he hath struck out Experiments, which he had tryed many years ago, because he since found them divulged by persons from whom he had not the least hint of them; which yet is not touched, with design to reflect upon any Ingenious Man, as if he were a Plagiary: For, though our Generous Author were not reserved enough in showing his Experiments to those that expressed a Curiosity to see them (amongst whom a very Learned Man hath been pleased publickly to acknowledge it several years ago[2]; yet the same thing may be well enough lighted on by persons that know nothing of one another. And especially Chymical Laboratories may many times afford the same _Phænomenon_ about Colours to several persons at the same or differing times. And as for the few _Phænomena_ mentioned in the same Chymical writers, as well as in the following Treatise, our Author hath given an account, why he did not decline rejecting them, in the Anotations upon the 47th Experiment of the third part. Not here to mention, what he elsewhere saith, to shew what use may be Justifiably made of Experiments not of his own devising by a writer of Natural History, if, what he employes of others mens, be well examined or verified by himself.