For mathematics the expression "almost eternal" is nothing tempting. Movement can be either eternal or finite; "almost eternal" means, in fact, finite.
But in practical life it is not. Many probably would be quite satisfied if they received at their disposal not quite perpetual motion, and "almost eternal, able to move at least, for example, for a thousand years. Human life is short, and the Millennium for us what eternity. People practical folds, probably would consider that the problem of perpetual motion resolved that no longer work to wrestle.
Such people can be good news message that 1000-year-old engine has already been invented; each may be under certain expenses to have the semblance of such eternal engine. The patent for this invention has not taken, and the secret he is not. The device, invented by Prof. Stretton in 1903 and is usually called "radium clock", is very easy.
Radium watch "almost eternal plant of 1600 years.
Inside glass jars, from which deflated the air, suspended on a quartz filament In (not conducting electricity) a small glass tube Andcomprising a few thousandths of a gram of radium salts. By the end of the tube is suspended, as in the electroscope, two gold leaf. Radium, as you know, emits rays of three genera: alpha rays, beta and gamma. In this case, the main role is played easily through the glass beta rays, which consist of a stream of negatively charged particles (electrons). Scatter radii in all directions, the particles carry a negative charge, and therefore the tube with radium gradually charged positively. This positive charge is transferred to the gold leaves and causes them to move apart.
Radinovich, leaves touch the walls of banks, is losing its charge (in the appropriate places of the walls of the glued strips of foil, on which the electricity is out) and closed again. Soon accumulated a new charge, the leaves diverge again, again give the charge to the walls and closed again to alectrosaurus. Every two or three minutes takes one swing gold leaves, with the regularity of the clock pendulum, hence the name "radium watch". So will last for years, decades, centuries, and will continue until the emission of radium rays.
The reader sees, of course, to him that is not "eternal", but only gratuitous engine.
How long does radium emits its rays? It is established that after 1600 years, the ability to emit rays of radium diminished by half. Therefore, radium watch will go nonstop for at least a thousand years, only gradually reducing the frequency of its vibrations, due to the weakening of the electric charge. If in the early days of Russia were arranged such radium watch, they would act in our time!
Can I use this type of engine for any practical purposes? Unfortunately, no. The power of this engine, i.e., the amount of work committed to them at the moment, so insignificant that no mechanism cannot operate them in action. In order to achieve any tangible results, it is necessary to have a much larger inventory of radium. If you remember that radium is extremely rare and expensive item, you will agree that gratuitous engine of this kind would be too costly.