Isaac Newton

**Sir Isaac Newton** (1642 to 1727) was an English mathematician, physicist, astronomer, and author, who was highly influential in the Scientific Revolution of the 17th century. He was the Lucasian Professor of Mathematics at the University of Cambridge and president of the Royal Society.

### Discoveries:

* His discovery of the composition of white light laid the foundation for modern physical optics. He showed how light can be analyzed into its components by reflection as well as refraction.
* His three laws of motion resulted in the formulation of the law of universal gravitation. It has famously been suggested that when Newton was sitting under an apple tree at Cambridge, seeing an apple fall triggered thoughts of gravity.
* In mathematics, he was the original discoverer of calculus, published in *Principia Mathematica.* Leibniz later arrived at calculus independently, although this was challenged and disputed by Newton.
* Invented and made the first reflecting telescope which used a mirror to collect starlight.

### Newton's Prism

When Newton was experimenting with lights and colors in the late 1660s, many contemporaries thought that colors were a mixture of light and darkness, and that prisms colored light. Despite the prevailing view, he became convinced that white light was not the single entity that Aristotle believed it to be but rather a mixture of many different rays corresponding to different colors.

In 1704, his work *Opticks* was published. In this work, Newton discusses his investigations of colors and the diffraction of light. Newton used triangular glass prisms in his experiments. Light enters one side of the prism and is refracted by the glass into various colors. Prisms work because light changes speed when it moves from air into the glass of the prism. Once the colors were separated, Newton used a second prism to refract them back together to form white light again. This experiment demonstrated that the prism was not simply adding colors to the light, as many believed. Newton also passed only the red color from one prism through a second prism and found the redness unchanged. This was further evidence that the prism did not create colors, but merely separated colors present in the original light beam.

### Halley's Comet

In 1066 a comet appeared over England and was interpreted as an omen that King Harold’s troops would be defeated at the Battle of Hastings. In 1682, that same comet reappeared. Newton used his reflecting telescope and documented the trajectories of several comets and compared them with predictions he had made according to his theory of universal gravitation, and applied this to the mysterious comet.

Edmond Halley the astronomer visited Cambridge to meet Newton and learnt that he was tracking comets and could predict their future motions, and realized this was one of the most monumental breakthroughs in all of science. He offered to pay for Principia Mathematica where calculus is used to determine the motion of the planets and comets in the solar system. He discovered that comets can travel in ellipses, in which case they might return. Halley, adopting Newton’s methods, calculated that the comet would return in the year 1758. When it did, it sealed Halley’s legacy and the comet was named after him.