George Berkeley
Berkeley argued that forces and gravity, as defined by Newton, constituted "occult qualities" that "expressed nothing distinctly". He held that those who posited "something unknown in a body of which they have no idea and which they call the principle of motion, are in fact simply stating that the principle of motion is unknown." Therefore, those who "affirm that active force, action, and the principle of motion are really in bodies are adopting an opinion not based on experience." Forces and gravity existed nowhere in the phenomenal world. On the other hand, if they resided in the category of "soul" or "incorporeal thing", they "do not properly belong to physics" as a matter. Berkeley thus concluded that forces lay beyond any kind of empirical observation and could not be a part of proper science. He proposed his theory of signs as a means to explain motion and matter without reference to the "occult qualities" of force and gravity.
Women in science
Émilie du Châtelet, a close friend of Voltaire, was the first scientist to appreciate the significance of kinetic energy, as opposed to momentum. She repeated and described the importance of an experiment originally devised by Willem 's Gravesande showing the impact of falling objects is proportional not to their velocity, but to the velocity squared. This understanding is considered to have made a profound contribution to Newtonian mechanics. In 1749 she completed the French translation of Newton's "Philosophiae Naturalis Principia Mathematica" (the "Principia"), including her derivation of the notion of conservation of energy from its principles of mechanics. Published ten years after her death, her translation and commentary of the "Principia" contributed to the completion of the scientific revolution in France and to its acceptance in Europe.