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 they have always agreed with the Sun. As to the Printing of the Figure of my New Watch, I shall defer that yet a while: but it shall in time appear with all the Demonstrations thereof, together with a Treatise of Pendulums, written by me some days since, which is of a very subtile Speculation.

It is the deservedly famous Monsieur de Fermat, who was, (saith the Author of the Letter) one of the most Excellent Men of this Age, a Genius so universal, and of so vast an extent, that if very knowing and learned Men had not given testimony of his extraordinary merit, what with truth can be said of him, would hardly be believed. He entertained a constant correspondence with many of the most Illustrious Mathematicians of Europe, and did excel in all the parts of Mathematical Science: a Testimony whereof he hath left behind him in the following Books.

A Method for the Quadrature of Parabola's of all degrees.

A Book De Maximis & Minimis, which serveth not only for the determination of Problems of Plains and Solids, but also for the invention of Tangents and Curve Lines, and of the Centres of Gravity in Solids; and likewise for Numerical Questions.

An Introduction to the Doctrine of Plains and Solids, which is an Analytical Treatise, concerning the solution of Plains and Solids, which has been seen (as the Advertiser affirms) before Monsieur Des Cartes had publish'd any thing upon this Subject.

A Treatise De Contactibus Sphæricis, where he hath demonstrated in Solids, what Mr. Viet, Master of Requests, had but demonstrated in Plains.

Another Treatise, wherein he establisheth and demonstrateth the two Books of Apollonius Pergæus, of Plains.

And a General Method for the dimension of Curve Lines, &c. Besides, having a perfect knowledge in Antiquity, he was consulted from all parts upon the difficulties that did emerge therein: he hath explained abundance of obscure places, that are found