To Explain the World: The Discovery of Modern Science by Steven Weinberg Page B

Barrow’s suggestion, the chair went to Newton. With financial help from his mother, Newton began to spread himself, buying new clothes and furnishings and doing a bit of gambling. 1
    A little earlier, immediately after the restoration of the Stuart monarchy in 1660, a society had been formed by a few Londoners including Boyle, Hooke, and the astronomer and architect Christopher Wren, who would meet to discuss natural philosophy and observe experiments. At the beginning it had just one foreign member, Christiaan Huygens. The society received a royal charter in 1662 as the Royal Society of London, and has remained Britain’s national academy of science. In 1672 Newton was elected to membership in the Royal Society, which he later served as president.
    In 1675 Newton faced a crisis. Eight years after beginning his fellowship, he had reached the point at which fellows of a Cambridge college were supposed to take holy orders in the Church of England. This would require swearing to belief in the doctrine of the Trinity, but that was impossible for Newton, who rejected the decision of the Council of Nicaea that the Father and the Son are of one substance. Fortunately, the deed that had established the Lucasian chair included a stipulation that its holder should not be active in the church, and on that basis King Charles II was induced to issue a decree that the holder of the Lucasian chair would thenceforth never be required to take holy orders. So Newton was able to continue at Cambridge.
    Let’s now take up the great work that Newton began at Cambridge in 1664. This research centered on optics, mathematics, and what later came to be called dynamics. His work in any one of these three areas would qualify him as one of the great scientists of history.
    Newton’s chief experimental achievements were concerned with optics. * His undergraduate notes, the Questiones quandam philosophicae , show him already concerned with the nature of light. Newton concluded, contrary to Descartes, that light is not a pressure on the eyes, for if it were then the sky would seem brighter to us when we are running. At Woolsthorpe in 1665 he developed his greatest contribution to optics, his theory of color. It had been known since antiquity that colors appear when light passes through a curved piece of glass, but it had generally been thought that these colors were somehow produced by the glass. Newton conjectured instead that white light consists of all the colors, and that the angle of refraction in glass or water depends slightly on the color, red light being bent somewhat less than blue light, so that the colors are separated when light passes througha prism or a raindrop. * This would explain what Descartes had not understood, the appearance of colors in the rainbow. To test this idea, Newton carried out two decisive experiments. First, after using a prism to create separate rays of blue and red light, he directed these rays separately into other prisms, and found no further dispersion into different colors. Next, with a clever arrangement of prisms, he managed to recombine all the different colors produced by refraction of white light, and found that when these colors are combined they produce white light.
    The dependence of the angle of refraction on color has the unfortunate consequence that the glass lenses in telescopes like those of Galileo, Kepler, and Huygens focus the different colors in white light differently, blurring the images of distant objects. To avoid this chromatic aberration Newton in 1669 invented a telescope in which light is initially focused by a curved mirror rather than by a glass lens. (The light rays are then deflected by a plane mirror out of the telescope to a glass eyepiece, so not all chromatic aberration was eliminated.) With a reflecting telescope only six inches long, he was able to achieve a magnification by 40 times. All major astronomical light-gathering telescopes are now reflecting telescopes, descendants