Lemma 14, concerning the motion of bodies in eccentric conic sections, from Newton's 'Principia Mathematica' (1687). The Lemma posits that: 'A perpendicular dropped from the focus of a parabola to its tangent is a mean proportional between the distance of the focus from the point of contact and its distance from the principle vortex of the figure.' The discoveries of English physicist and mathematician Isaac Newton (1642-1727) were prolific and hugely influential on science and thought. His work included the three laws of motion, the theory of gravitation, the law of cooling, the binomial theorem and the calculus.
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