Lemma 27, to find orbits when neither focus is given, from Newton's 'Principia Mathematica' (1687). The Lemma posits that: 'To describe a quadrilateral given in species, whose corners will lie on four straight lines, given in position, which are not all parallel and do not all converge to a common point - each corner lying on a separate line.' 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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