Page:Philosophical Transactions - Volume 001.djvu/408

 it somewhat of a Sky-colour, he was, upon owning his surprise thereat, informed, that a dozen of them being put in, they would dye it to almost a full Azure. Which is touch't here, that, the Experiment being so easie to make, it may be tried, when the season furnishes those Insects; mean time, it seems not more incredible, that this Creature should yield a Sky-colour, when put in water, than that Cochineel, which also is but an Insect, should afford a fine red, when steep'd in the same Liquor.

An Account Of Some Books.

As the two first Tomes of M. Des-Cartes his Letters, contain Questions, for the most part of a Moral and Physiological Nature, proposed to, and answer'd by him; so this consists of the Contests, he had upon several Subjects with divers Men eminent in his time.

To pass by that sharp Contest, he was engaged in by some Professors of Divinity at Utrecht, who endeavoured to discredit his Philosophy, as leading to Libertinisme and Atheisme, notwithstanding he made it so much his business, to assert the Existence of a Deity, and the Immortality  of a Soul: We shall take notice of what is more to our purpose, vid., the Differences, he had touching his Dioptricks and Geometry.

As for his Dioptricks, though a great part of the Learned World have much esteem'd that Treatise, as leaving little to be said after him upon that Subject; yet there have not been wanting Mathematicians, who have declared their disagreement from his Principles in that Doctrine, The first of them was the Jesuit Boudrin, Mathematick Professor in the Colledg of Clermont at Paris; but this difference was soon at an end. A second was Mr. Hobbs, upon whose account he wrote several Letters to Mersennus, containing many remarks conducing to the Knowledge of the Nature of Reflection and Refraction. But the Person, that did most learnedly and resolutely attack the said Dioptricks, was Monsieur Fermat, Rh Errata