Isaac Newton
... philosophers believed that white light was a homogenous entity. Newton reached a revolutionary conclusion that this is not so. He noted that when a beam of sunlight passes through a glass prism that the colors- red, yellow, green, blue, and violet formed on the opposite wall. The old theory stated that all rays of white light striking the prism at the same angle would be equally refracted, but Newton argued that light is really a mixture of rays refracted at different angles. Each ray produced a given spectral color. Newton performed an experiment which he selected one narrow band of light of on color out of a prism and found no further elongnation occured. All the selected rays of one color were refracted at the same angle. This all led Newton to conclude that telescopes using refracting lenses could never overcome distortions of chromatic dispersion. Therefore, he constructed a reflection telescope. This was the first of its kind, and the prototype of the largest modern optical telescopes. Newton’s greatest achievement was his work in physics and celestial mechanics, which brought him the theory of universal gravitation. The story of Newton discovering the theory of gravitation was in 1666 when he watched an apple fall from a tree in his garden even though he started in the plague years. He had discovered the law of centrifugal force (the force away from the center) of a body moving uniformly in a circular path. The other is centripetal force (toward the center)- rather than as the result of one force, a centripetal force, which constantly deflects the body away from its inertial path in a straight line. Newton’s great insight was to imagine that the earth’s gravity extended to the Moon, counterbalancing its centrifugal force. From his law of centrifugal force, Newton deduced that the centrifugal force of the Moon or of any planet must decrease as the inverse square of its distance from the center of its motion. In 1679 Robert Hooke presented Newton the problem of orbital motion. Hooke is credited with suggesting to Newton that circular motion arises from the centripetal deflection of inertially moving bodies. Hooke further conjectured that since the planets move in ellipses with the Sun at one focus, the centripetal force drawing them to the Sun should vary as the inverse square of their distances from it. Hooke could not prove this theory mathematically, but Newton did. He showed that if a body obeys Kepler’s second law (which states that the line joining a planet to the Sun sweeps out equal areas in equal times), then the body is being acted upon by a centripetal force. With this, Newton revealed the significanse of Kepler’s second law. Newton’s principia is said to be the greatest scientific book ever written. In the book, Newton fully analyze...