An Answer (to the former Letter,) written to the Publisher June 10. 1673. by the same Parisian Philosopher, that was lately said to have written the Letter already extant in No. 96. p. 6086.

TOuching the Solutions, given by M. Newton to the scruples by me propos'd about his Theory of Colors, there were matter to answer them, and to form new difficulties; but seeing that he maintains his opinion with so much concern, I list not to dispute. But what means it, I pray, that he saith; Though I should shew him, that the White could be produced of only two Un-compounded colors, yet I could conclude nothing from that. And yet he hath affirm'd in p. 3083. of the Transactions, that to compose the White, all primitive colors are necessary.

As to the manner, whereby he reconciles the effect of Convex glasses for so well assembling the rays, with what he establishes concerning the different refrangibility, I am satisfied with it; but then he is also to acknowledge, that this aberration of the rays is not so disadvantagious to Optic glasses as he seems to have been willing to make us believe, when he proposed Concave speculums as the only hopes of perfecting Telescopes. His invention certainly was very good; but, as far as I could perceive by experience, the defect of the Matter renders it as impossible to execute, as the difficulty of the Form obstructs the use of the Hyperbole of M. Des-Cartes: So that, in my opinion, we must stick to our Spheric Glasses, whom we are already so much obliged to, and that are yet capable of greater perfection, as well as by increasing the length of Telescopes, as by correcing the nature of Glass it self. So far He.

To this Letter is to be referr'd that, which is already extant in N. 96. p. 6087. as being an Answer thereto.