Since Antiquity humans have been fascinated by the motion of the stars in the celestial sphere. They hoped to imitate this motion and build a machine that would run forever without using an external force, such as wind or flowing water.
Many believed that rotation is an intrinsic property of the wheel. Even the Polish astronomer Copernicus believed that anything round –– according to him the perfect shape –– would rotate by itself. One of the early attempts to build a perpetually turning wheel can be found in a Sanskrit manuscript of the fifth century. It describes a wheel with sealed cavities in which mercury would flow in such a fashion that one half of the wheel would always be heavier than the other half; supposedly this would keep the wheel running. Around 1235 the French architect Villard de Honnecourt devised a wheel based on a similar principle. An odd number of hammers pivot around their attachment points on the wheel. Because one half of the wheel always has a larger number of hammers than the other half, the wheel would keep turning.
These devices existed in theory only, since any actual machine of this type fails to operate. It was during the Renaissance that engineers became seriously interested in building a machine that would produce power continuously. They were inspired by the large number of windmills and water wheels that were then in use. The concepts were simple: A water wheel drives a pump that continuously pumps up the water that runs the wheel into an elevated reservoir, or a windmill actuates giant bellows that drive the windmill.
Many other designs made their appearance. Some were systems in which water would keep flowing endlessly. Others were complicated mechanisms. In one type, steel balls roll down an inclined plane. The inclined plane pivots when the ball reaches its end. This motion then actuates a mechanism that brings the ball back to its beginning position on the inclined plane.
The first to formulate precisely why such perpetual-motion machines could not work was Gottfried Wilhelm Leibniz, who in his “Essay on Dynamics” stated that energy could not be created out of nothing. Although Leibniz’s idea was not paid much attention, by the end of the 18th century most scientists had concluded that perpetual-motion machines could not work. The Paris Academy decided to reject any proposals for perpetual-motion machines. All such devices neglect the loss of power to friction within the parts and often other factors that prevent functioning. Notwithstanding, inventors continue to propose perpetual-motion machines right up to present.