Natural Philosophy Including Mathematics, Optics, and Alchemy
In Newton's day, the term "natural philosophy" referred to the physical sciences, and Newton's work in this area was informed by his belief in a universe which operated on mechanical principles and which was set into motion by God. His scientific study focused on identifying the nature of these mechanical principles. In the course of this study, Newton discovered, developed, and elucidated the mathematical rules by which motion is governed; the fruits of this labor are presented in Philosophiae Naturalis Principia Mathematica (1687). Newton also sought to examine through extensive experimentation the properties of light and color, and his findings are published in Opticks (1704). modern critics analyze and debate Newton's scientific and mathematical achievements as evidenced by these two works as well as by several of Newton's unpublished papers. Another area of critical discussion focuses on the historical sources that may have influenced Newton's work. Newton's interest in alchemy has proved to be a topic of controversy among critics, as many students and scholars of Newton find it difficult to reconcile his rational, scientific work with a subject deemed occult and false.
Many of the calculations found in Principia were worked out by Newton many years earlier, after he had returned to his home in Woolsthorpe, when Trinity College closed due to the plague in 1665. In 1684 astronomer Edmund Halley approached Newton, asking him to describe the orbit of the planets. Newton responded that he had mathematically determined the orbit to be elliptical. Halley urged Newton to send him the calculations, which Newton did. With Halley's encouragement and patronage, Newton elaborated and expanded the work, which became the Principia. In this work, Newton explains the laws of the motion of the planets, moons, comets, the tides, and the earth. He also presents his theory of universal gravitation. The differential calculus Newton had earlier developed became a tool used for the calculations in Principia. In Opticks, Newton presents the results of his experiments with prisms, in which he had broken down white light into a spectrum of primary colors. This led to his theory that light was comprised of individual particles, or corpuscles. Also described in Opticks are Newton's experiments with colors of thin films. These experiments led to his theory that light could be both reflected and refracted. Additionally, Opticks contained a list of "Queries," in which Newton speculates not only about light and color, but other subjects of physics and philosophy as well.
Modern critics have continued to assess the relevance and significance of Newton's mathematical and scientific achievements. After noting the influence of Johannes Kepler and Galileo on Newton, Albert Einstein examined Newton's approach to the problem of motion and comments on the importance of Newton's findings. Einstein noted that while the theories of electromagnetic fields and relativity have limited the significance of some of Newton's work, Newton's mechanics nevertheless paved the way in other areas, making a theory of fields possible. Unlike Einstein, Brian Ellis has argued that Newton's laws of motion are more historically related to Cartesian physics than to Galileo's work in kinematics. In addition to demonstrating Newton's debt to René Descartes, Ellis also emphasizes the conceptual nature of Newton's laws of motion, arguing that they are not deduced from or supported by observation or experimentation. Rupert Hall and Marie Boas Hall center their study on Newton's theory of matter, maintaining that his unpublished manuscripts on this subject help to demonstrate the development of his theory. The critics discussed Newton's exploration of the role of aether in the movement of particles and commented on the influence of Newton's theological beliefs on his theory of matter. Critics such as Robert B. Downs...
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