There is absolutely no rest in Nature--everything is constantly changing--moving--and vibrating. Building-up processes are ever at work forming larger masses or bodies of the Particles--and tearing-down processes, disintegration and decomposition of Molecules and Atoms, and Corpuscles, are constantly at work also. Nature maintains a constant balance among her Forces. If the building-up energies and forces were allowed full sway, then all the Particles in the Universe ultimately would gravitate to a common centre, thus forming a compact and solid Mass, which would thus dwell for Eternity, unless the Creative Power should move upon it and again scatter its Particles in all directions. And, if the tearing-down, and dispersive forces and energies were allowed full sway, the Particles would fly apart and would remain asunder for Eternity, unless called together by some new Creative fiat. But Nature pits one force against another, maintaining an equilibrium. The result is constant play and inter-play of forces, causing distribution, and redistribution of Particles, following the gathering-together and building-up processes. There is no lost motion, or waste force. One form of force and motion is converted into another, and so on, and on. Nothing is lost--all force is conserved, as we shall see as we proceed. In the public mind--or rather, in the mind of that part of the public which think of the matter at all--there seems to be an idea that "Force" is something of the nature of an entity, separate from Substance or Mind--something that pounces down upon Substance and drives it along by presence from without. The ancient philosophers regarded Substance as acted upon from _without_ by an entity called Force, Substance being regarded as absolutely inert and "dead." This idea, which is still held by the average person, owing, doubtless, to the survival of old forms of expression, was generally held by philosophers until the time of Descartes and Newton. This old idea was due to the teachings of Aristotle--he of the Ether Theory--and Science and Philosophy were timid about shaking off the Aristotelian dogmas. Others held that Light, Heat and Electricity were "fluids" conveyed from body to body--in fact the general public still entertains this idea regarding Electricity, owing to the use of the term "the Electric _fluid_."