The overbalancing wheel perpetual motion seems to be as old as the 13th century. Dircks quotes an account of an invention by Wilars de Honecort, an architect whose sketchbook is still pre served in the Ecoles des Chartes at Paris. De Honecort says, "Many a time have skilful workmen tried to contrive a wheel that shall turn of itself ; here is a way to do it by means of an uneven number of mallets, or by quicksilver." He thereupon gives a rude sketch of a wheel with mallets jointed to its circumference. It appears that Leonardo da Vinci worked with similar notions.
Another scheme of the perpetual motionist is a water-wheel which shall feed its own mill-stream. This notion is probably as old as the first miller who experienced the difficulty of a dry season. One form is figured in the Mathematical Magic (1648) of Bishop Wilkins (1614-1672) ; the essential part of it is the water screw of Archimedes, which appears in many of the earlier ma chines of this class. Some of the later ones dispense with even the subtlety of the water-screw, and boldly represent a water wheel pumping the water upon its own buckets.
Perpetual motions founded on the hydrostatical paradox are not uncommon ; Denis Papin exposes one of these in the Philo sophical Transactions for 1685. The most naive of these devices is that illustrated in fig. 2, the idea of which is that the larger quantity of water in the wider part of the vessel weighing more will overbalance the smaller quantity in the narrower part, so that the water will run over at C, and so on continually.
Capillary attraction has also been a fav orite field for the vain quest ; for, if by cap illary action fluids can be made to disobey the law of never rising above their own level, what so easy as thus to produce a continual ascent and overflow, and thus per petual motion? Various schemes of this kind, involving an endless band which should raise more water by its capillary action on one side than on the other, have been proposed. The most celebrated is that of Sir William Congreve (1772-1828). EFG (fig. 3) is an inclined plane over pulleys; at the top and bottom travels an endless band of sponge, abed, and over this again an endless band of heavy weights jointed together. The whole stands over the surface of still water. The capillary action raises the water in ab, whereas the same thing cannot happen in the part ad, since the weights squeeze the water out. Hence, inch for inch, ab is heavier than ad; but we know that if ab were only just as heavy inch for inch as ad there would be equilibrium, if the heavy chain be also uniform; therefore the extra weight of ab will cause the chain to move round continually in the direction of the arrow.
The more recondite vehicles of energy, such as electricity and magnetism, are more seldom drawn upon by perpetual-motion in ventors than might perhaps be expected. William Gilbert, in his
treatise De Magnete, alludes to some of them, and Bishop Wilkins mentions among others a machine "wherein a loadstone is so dis posed that it shall draw unto it on a reclined plane a bullet of steel, which, still, as it ascends near to the loadstone, may be contrived to fall through some hole in the plane and so to return unto the place whence at first it began to move, and being there, the loadstone will again attract it upwards, till, coming to this hole, it will fall down again, and so the motion shall be perpetual." The fact that screens do exist whereby electrical and magnetic action can be cut off would seem to open a door for the perpetual motion seeker. Unfortunately the bringing up and removing of these screens involves in all cases just that gain or loss of work which is demanded by the law of the conservation of energy. A shoemaker of Linlithgow called Spence pretended that he had found a black substance which in tercepted magnetic attraction and repulsion, and he produced two machines which were moved, as he asserted, by the agency of permanent magnets, thanks to the black substance. The fraud was speedily exposed, but it is worthy of remark that Sir David Brew ster thought the thing worth men tioning in a letter to the Annales de chimie (1818), wherein he states "that Mr. Playfair and Cap , tain Dater have inspected both of these machines and are satisfied that they resolve the problem of perpetual motion." One more page from this chapter of the book of human folly; the author is the famous Jean Bernoulli the elder. We translate his Latin, as far as possible, into modern phraseology. In the first place we must premise the following. (See fig. 4.) (I) If there be two fluids of different densities whose densities are in the ratio of G to L, the height of equiponderating cylinders on equal bases will be in the inverse ratio of L to G. (2) Accordingly, if the height AC of one fluid, contained in the vase AD, be in this ratio to the height EF of the other liquid, which is in a tube open at both ends, the liquids so placed will remain at rest. (3) Where fore, if AC be to EF in a greater ratio than L to G, the liquid in the tube will ascend; or if the tube be not sufficiently long the liquid will overflow at the orifice E (this follows from hydrostatic principles). (4) It is possible to have two liquids of different density that will mix. (5) It is possible to have a filter, colander, or other separator, by means of which the lighter liquid mixed with the heavier may be separated again therefrom.