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 ago²; 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 47^th 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.

In the mean time, this Treatise is such, that there needs no other invitation to peruse it, but that tis composed by one of the Deepest & Most indefatigable searchers of Nature, which, I think the World, as far as I know it, affords. For mine own part, I feel a Secret Joy within me, to see such beginings upon such Themes, it being demonstratively true, Mota facilius moveri, which causeth me to entertain strong hopes, that this Illustrious Virtuoso and Restless Inquirer into Nature's Secrets will not stop here, but go on and prosper in the Disquisition or the other principal Colours, Green, Red, and Yellow. The Reasoning faculty set once afloat, will be carried on, and that with ease, especially, when the productions thereof meet, as they do here, with so greedy an Entertainment at home and abroad. I am confident, that the ROYAL SOCIETY, lately constituted by his MOST EXCELLENT MAJESTY for improving Natural knowledge, will Judge it their interest to exhort our Author to the prosecution of this Argument, considering, how much it is their design and business to accumulate a good stock of such accurate Observations and Experiments, as may afford them and their Offpring genuine Matter to raise a Masculine Philosophy upon, whereby the Mind of Man may be enobled with the Knowledge of solid Truths, and the Life of Man benefited with ampler accommodations, than it hath been hitherto.

Our Great Author, one of the Pillars of that Illustrious Corporation, is constantly furnishing large Symbola's to this work, and is now falln, as you see, upon so comprehensive and important a theme, as will, if insisted on and compleated, prove one of the considerablest peeces of that structure. To which, if he shall please to add his Treatise of Heat and Flame, as he is ready to publish his Experimental Accounts of Cold, I esteem, the World will be obliged to Him for having shewed them both the Right and Left Hand of Nature, and the Operations thereof.

The considering Reader will by this very Treatise see abundant cause to sollicit the Author for more; sure I am, that of whatever of the Productions of his Ingeny comes into Forein parts (where I am happy in the acquaintance of many intelligent friends) is highly valued; And to my knowledge, there are those among the French, that have lately begun to learn English, on purpose to enable themselves to read his Books, being impatient of their Traduction into Latin. If I durst say all, I know of the Elogies received by me from abroad concerning Him, I should perhaps make this Preamble too prolix, and certainly offend the modesty of our Author.

Wherefore I shall leave this, and conclude with desiring the Reader, that if he meet with other faults besides those, that the Errata take notice of (as I believe he may) he will please to consider both the weakness of the Authors eyes, for not reviewing, and the manifold Avocations of the Publisher for not doing his part; who taketh his leave with inviting those, that have also considered this Nice subject experimentally, to follow the Example of our Noble Author, and impart such and the like performances to the now very inquisitive world. Farewell.

H. O.

THE
CONTENTS.

CHAP. I.

The Author shews the Reason, first of his Writing on this Subject (1.) Next of his present manner of Handling it, and why he partly declines a Methodical way (2.) and why he has partly made use of it in the History of Whiteness and Blackness. (3.)

Chap. 2. Some general Considerations are premis'd, first of the Insignificancy of the Observasion of Colours in many Bodies (4, 5.) and the Importance of it in others (5.) as particularly in the Tempering of Steel (6, 7, 8.) The reason why other particular Instances are in that place omitted (9) A necessary distinction about Colour premis'd (10, 11.) That Colour is not Inherent in the Object (11.) prov'd first by the Phantasms of Colours to Dreaming men, and Lunaticks; Secondly by the sensation or apparition of Light upon a Blow given the Eye or the Distemper of the Brain from internal Vapours (12.) The Author recites a particular Instance in himself; another