Cartesian Lumière and Newtonian Light

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Dean Langley


My thesis examines the scientific methods of René Descartes and Sir Isaac Newton. I begin by looking briefly at Aristotle's concept of light. Aristotle believed that light was a property that the medium acquired instantaneously from a luminous source. Descartes later separated light from the medium and the luminous object as in instantaneous pression in the ether. He introduced a more mechanical way of examining light with this separation. Descartes' methods consist mainly of analogies between the behavior of light and observations of processes unrelated to optics. Descartes appears to have derived the law of refraction. This law is a very important result in optics. Historians debate whether Descartes was the original discoverer of the law, or if Snell found it first and Descartes plagiarized him. After examining Descartes' methods, I turn to Newton's methods. Newton made suppositions about the behavior of light and supported them with experiments. Newton believed that light was a particle with certain unchangeable characteristics, such as refrangibility and color. He studied the formation of colored rings in thin films. He improved telescopes using reflection and refraction. To understand Newton's methods better, I performed some of his experiments and observed the rings in thin films of air and soapy water. I report my results and compare them with Newton's. I describe the telescope I built. I also analyze some of Newton's Queries, using modern optical knowledge. I conclude by summarizing the impact that Descartes and Newton had on the development of optical theory.

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