During his time in Woolsthorpe, Newton developed his method of 'fluxions' (what we now call calculus), a powerful mathematical tool for solving problems involving rates of change and areas under curves. He initially kept this discovery largely to himself.

Newton conducted experiments with prisms, demonstrating that white light is composed of a spectrum of colors. He proposed that color is not a modification of light, but rather an inherent property of light itself. This led him to develop the reflecting telescope to avoid chromatic aberration.

Newton formulated his law of universal gravitation, which states that every particle of matter in the universe attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This explained the motion of planets and falling objects on Earth with a single, universal law.

Newton's "Philosophiæ Naturalis Principia Mathematica" (Mathematical Principles of Natural Philosophy) was published. This monumental work laid the foundation for classical mechanics and presented his laws of motion and law of universal gravitation. It is widely regarded as one of the most important scientific books ever written.

Newton published "Opticks", a comprehensive treatise on his work in optics. It detailed his experiments with prisms, his theory of color, and his ideas about the nature of light. The book was written in English, making it more accessible to a wider audience than the "Principia".