Chap. 3. PHILOSOPHICAL DISCOVERIES.

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He did no less service by treating, in a clear and geome-trical manner, the doctrine of motion, which has been justlycalled the key of nature. The rational part of mechanics hadbeen so much neglected, that there was hardly any improve-ment made in it, from the time of the incomparable Archi-j?iedes to that of Galileo ; but this last named author has givenus fully the theory of equable motions, and of such as areuniformly accelerated or retarded, and of these two com-pounded together. He, first, demonstrated, that the spacesdescribed by heavy bodies from the beginning of their descentare as the squares of the times, and that a body, projectedin any direction that is not perpendicular to the horizon, de-scribes a parabola. These were the beginnings of the doctrineof the motion of heavy bodies, which has been since carried toso great a height by Sir Isaac Newton.

He also discovered the gravity of the air, and endeavouredto compare it with that of water ; and opened up severalother enquiries in natural philosophy. He was not esteem’d.and followed by philosophers only, but was honoured by per-sons of the greatest distinction of all nations. Des Cartes ,indeed, * after commending him for applying geometry tophysics, complains that he had not examined things in order,but had enquired into the reasons of particular effects only ;adding that, by his pasting over the primary causes of nature,he had built without a foundation. He did not, ’tis true, takeso high a flight as Des Cartes , or attempt so universal a system;but this complaint, I doubt, must turn out to Galileos praise ;while the censure of Des Cartes shews that he had the weaknessto be vain of the worst part of his writings.

* Epistol. part 2. epist. 91.

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