الوسم: الحركة

Perpetual Futility
A short history of the search for perpetual motion.
by Donald E. Simanek
Popular histories too often present perpetual motion machines as “freaks and curiosities” of engineering without telling us just how they were understood at the time. They also fail to inform us that even in the earliest history of science and engineering, many persons were able to see the futility and folly of attempts to achieve perpetual motion.
Sometimes a particular device comes to us with a label, such as “Bishop Wilkins’ magnetic perpetual motion machine.” Popular articles leave the impression that the inventor believed it was a perpetual motion machine. In fact, very often the device was presented and described to illustrate the futility of the quest for perpetual motion.

Bhaskara Wheel.
GIF by Hans-Peter GramatkeBhaskara Wheel
with curved spokes.
The first documented perpetual motion machines were described by the Indian author Bhaskara (c. 1159). One was a wheel with containers of mercury around its rim. As the wheel turned, the mercury was supposed to move within the containers in such a way that the wheel would always be heavier on one side of the axle. Perhaps this was not so much a practical proposal as an illustration of Indian cyclical philosophy. The idea reappears in Arabic writings, one of which contained six perpetual motion devices. From the Islamic world the idea reached Europe.

Villard’s Wheel.
Villard de Honnecourt was born in the late 12th century and probably lived and worked in the north of France from 1225 to 1250. His sketchbook of 33 parchment leaves with 250 drawings has survived, and now is in the Bibliiothèque Nationale in Paris. These show designs for churches, catapults mechanisms and machines. Villard is often called an architect, but we know of no structure that he designed, or that is attributed to him. He traveled a lot, but we are not sure what he did for a living.
The most celebrated of his machine designs was for a perpetual motion wheel. It was an overbalanced wheel with hinged hammers or mallets equally spaced around its rim. The picture displays ambiguous perspective. The wheel is actually supposed to be perpendicular to the frame and to the horizontal axle. It also shows unequal spacing of the hammer pivots around the wheel. Perhaps it was intended as “schematic only”. The upper two hammers in particular seem inconsistent. Compared to Villard’s other drawings, this one is singularly “sketchy” and carelessly executed. Villard’s description (translated) is:

Many a time have skilful workmen tried to contrive a wheel that should turn of itself; here is a way to make such a one, by means of an uneven ****** of mallets, or by quicksilver (mercury).

The reference to quicksilver (mercury) indicates that Villard was familiar with the Bhaskara device, whose design had reached Europe. Villard claimed his machine would be useful for sawing wood and raising weights.
Villard’s diagram shows seven hammers, and he insisted on an odd (uneven) ****** of hammers, explaining

…there will always be four on the downward side of the wheel and only three on the upward side; thus the mallet or bag will always fall over to the left as it reaches the top, ad infinitum.

But, whether the ****** of hammers is odd or even, such a wheel comes to rest quickly. This design was copied many times, often with an even ****** of hammers.