Galileo died in Italy on January, 1642, and on December 25th of that same year, Isaac Newton was born in Lincolnshire, England. He became one of the most influential and distinguished scientists of all time. Remembered for physics, mathematics and astronomy, he also worked on alchemy and theology. He was a bridge between the mediaeval and modern worlds.
Newton's main contribution was to show that the workings of the world could be understood in terms of rational laws, and the same laws that explained the behaviour of objects on Earth also regulated the most distant part of the heavens. Where people had separated existence into two domains, the Earth and the Heavens, Newton showed that they were one.
He wondered why apples separated from trees always moved in the same direction, towards the ground, and postulated that a force might be acting on them. He wondered if that force might apply to all bodies, not only those we see on Earth, but also including the distant ones we see in the heavens. Encouraged by the Astronomer Royal, Sir Edmund Halley, he published his famous "Principia," laying the groundwork of classical mechanics.
Having devised the theory of gravity, he used it to prove mathematically Kepler's empirical laws of planetary motion. He also explained tidal motions, the trajectories of comets and the precession of the equinoxes. The idea that humankind could gain knowledge of a rational and ordered universe laid the basis for the intellectual Enlightenment which followed.
Newton showed that natural laws governed the behaviour of light, using a prism to split white light into it coloured components. Realizing that telescope lenses would always have colour distortion, Newton invented the reflecting telescope that bears his name, grinding the mirror and the eyepieces himself.
He used his mathematical 'fluxions' - differential and integral calculus (invented independently by Leibniz) to mathematicize other physical sciences, and he set out the systematic basis for a scientific method based on observation and experiment.
He was a fellow at Trinity College, Cambridge, then a professor there, requiring Royal dispensation to do so without taking Holy Orders. He served two terms as MP for the University, and was knighted by Queen Anne in 1705. He was Master of the Royal Mint, and President of the Royal Society.
Although Einstein's relativity has made Newtonian mechanics into a special case, his laws still dominate the explanations of most of what we observe. Newton encouraged us and enabled us to be bold. Today when we seek explanations of observed phenomena, it is because Newton taught us that we could do so, and also taught us how to do so. The test is not theory, something dreamed up in the mind. The test is observation, and if the observation does not bear out the theory, we change it or discard it. The universe is no longer a mystery to be gazed at in uncomprehending awe. It is something we can grasp and can understand, and something that we can predict. Newton's ideas still live.