Isaac Newton uses a prism to split sunlight into the component colours of the optical spectrum, assisting understanding of the nature of light.
Robert Hooke and Giovanni Alfonso Borelli both expound gravitation as an attractive force (Hooke's lecture "On gravity" at the Royal Society of London on March 21; Borelli's Theoricae Mediceorum planetarum ex causis physicis deductae, published in Florence later in the year).