Bunch-Hellemans, Perpetual motion as a 19th-century obsession

During the 19th century, with the advent of electricity, inventors planned and sometimes built machines in which an electric motor drove a generator that, in turn, supplied power to the electric motor. The goal was perpetual motion and a “free” source of energy. A large number of other designs, some very intricate and based on hydraulic, pneumatic, and magnetic forces, appeared at that time with the same purpose.

None of these machines fulfilled their promise. Some seemed to work, but invariably they were found to be hoaxes. Also during the 19th century, scientists discovered why perpetual motion machines would not work when they learned the law of conservation of energy. Until then, the quest for free energy became comparable to the UFO obsession during the 20th century. Several inventors cashed in by building complicated machines and charging admission for demonstrations or receiving funding for their inventions.

A famous case was that of Charles Redheffer, who, at the beginning of the 19th century, displayed a perpetual motion machine in his house in Philadelphia, Pennsylvania, charging admission fees and receiving funding. Redheffer was soon found out because a young boy noticed that the teeth on a cogwheel were worn on the wrong side, showing that the machine was driven by an external power source. Redheffer promptly moved his show to New York City, where he was unmasked by the famous engineer Robert Fulton, who, upon seeing the machine, exclaimed, “Why, this is a crank motion!” Fulton had noticed an irregularity in the rotation of the machine, the telltale sign of a manually driven crank.

But some perpetual motion machines were bona fide attempts at extracting energy from the forces of nature. The Zeromotor was a famous project of a British professor, John Gamgee. His idea was based on replacing water in a steam engine with ammonia, a liquid that boils at –433.5°C (–31.9°F). He reasoned that the ambient heat would cause the ammonia to boil. Even at a temperature as low as 0°C (32°F), boiling ammonia turns to a gas that increases in volume enough to produce 4 atmospheres of pressure, sufficient to drive a piston in a cylinder. During expansion in the cylinder, Gamgee believed, the ammonia gas would condense and the resulting liquid could be pumped back to the “boiler.” In practice, the gas did not liquefy, and the Zeromotor did not work. What Gamgee had overlooked was that the ammonia gas would condense only if the cylinder had cooled below the boiling point of ammonia, back below to –33.5°C. Unfortunately, the energy required to cool the cylinder would be greater than the amount the machine could supply. Just as in all other perpetual motion machines, there was a hitch. As in most such cases, the hitch was the second law of thermodynamics, the rule that heat always flows from warmer places to cooler ones unless some outside energy is applied to reverse the flow. A version of this law discovered by the French engineer Sadi Carnot in 1824 is that the most energy available from a process is fixed by differences in heat energy.

Understanding of the laws of thermodynamics made it clear to scientists that a machine that can supply power from nothing is a physical impossibility. Notwithstanding, intrepid inventors are still building perpetual motion machines today.


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