554 PERPETUAL MOTION necessary, it must proceed by induction from all physical phenomena. It would serve no useful purpose here to give an exhaustive historical account of the vagaries of mankind in pursuit of the "perpetuum mobile." The reader may consult on this subject the two volumes by Henry Dircks, C.E., published by E. and F. N. Spon, London, 1861 and 1870, from which, for the most part, we select the follow ing facts to give the reader some idea of this department of the history of human fallibility. By far the most numerous class of perpetual motions is that which seeks to utilize the action of gravity upon rigid solids. We have not read of any actual proposal of the kind, but the most obvious thing to imagine in this way would be to procure some substance which intercepts gravitational attraction. If this could be had, then, by introducing a plate of it underneath a body while it was raised, we could elevate the body without doing work ; then, removing the plate, we could allow the body to fall and do work ; eccentrics or other imposing device being added to move the gravitation intercepter, behold a perpetual motion complete ! The great difficulty is that no one has found the proper material for an intercepter. Fig. 1 represents one of the most ancient and oftenest- repeated of gravitational perpetual motions. The idea is that the balls rolling in the compartments between the felloe and the rim of the wheel will, on the whole, so com port themselves that the moment about the centre of those on the descending side exceeds the moment of those on the ascending side. Endless devices, such as curved spokes, levers with elbow- joints, eccentrics, itc., have been proposed for effecting this impossibi- // NV" ^~ ::::: . lity. The modern student 1 1 XsQl K x) I 4- of dynamics at once con vinces himself that no machinery can effect any such result ; because, if we give the wheel a com plete turn, so that each ball returns to its ori ginal position, the whole work done by the ball will, at the most, equal that done on it. If we were to start the wheel and balls in the most general way possible, we should doubtless have a very pretty problem to solve ; but we know that, if the laws of motion be true, in each step the kinetic energy given to the whole system of wheel and balls is equal to that taken from the potential energy of the balls less what is dissipated in the form of heat by frictional forces, or vice versa, if the wheel and balls be losing kinetic energy, save that the friction in both cases leads to dissipation. So that, whatever the system may lose, it can, after it is left to itself, never gain energy during its motion. The two most famous perpetual motions of history, viz., the wheels of the marquis of Worcester and of Councillor Orffyreus were, probably of this type. The marquis of Worcester gives the following account of his machine in his Century of Inventions (art. 56). " To provide and make that all the "Weights of the descending side of a Wheel shall be perpetually further from the Centre than those of the mounting side, and yet equal in number and heft to the one side as the other. A most incredible thing, if not seen, but tried before the late king (of blessed memory) in the Tower, by my directions, two Extraordinary Embassadors accompanying His Majesty, and the Duke of Richmond, and Duke Hamilton, with most of the Court, attending Him. The Wheel was 14. Foot over, and 40. Weights of 50. pounds apiece. Sir William Bed/ore, then Lieutenant of the Tower, can justify it, with several others. They all saw, that no sooner these great Weights passed the Diameter- line of the lower side, but they hung a foot further from the Centre, nor no sooner passed the Diameter-line of the upper side but they hung a foot nearer. Be pleased to judge the consequence." Orffyreus (whose real name was Bessler) also obtained distinguished patronage for his invention. His last wheel, for he appears to have constructed more than one, was 12 feet in diameter and 1 foot 2 inches broad ; it consisted of a light framework of wood covered in with oil-cloth so that the interior was concealed, and was mounted on an axle which had no visible connexion with any external mover. It was examined and approved of by the land grave of Hesse-Cassel, in whose castle at Weissenstein it is said to have gone for eight weeks in a sealed room. The most remarkable thing about this machine is that it evidently imposed upon the mathematician s Gravesande, .who wrote a letter to Newton giving an account of his examination of Orffyreus s wheel undertaken at the request of the landgrave, wherein he professes himself dissatisfied with the proofs theretofore given of the impossibility of perpetual motion, and indicates his opinion that the in vention of Orffyreus is worthy of investigation. He him self, however, was not allowed to examine the interior of the wheel. The inventor seems to have destroyed it himself. One story is that he did so on account of diffi culties with the landgrave s Government as to a licence for it ; another that he was annoyed at the examination by s Gravesande, and wrote on the wall of the room containing the fragments of his model that he had destroyed it because of the impertinent curiosity of Professor s Gravesande. The history of this case is noteworthy, because it con tains all the characters that usually appear in such comedies even now, the fraudulent paradoxer, the illustrious and intelligent patron, the simple-minded, unbiassed, scientific witness. It is worthy of remark that the overbalancing -wheel perpetual motion seems to be as old as the 13th century. In his second series Dircks quotes an account of an inven tion by Wilars de Honecort, an architect whose sketch-book is still preserved 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 would appear from some of the manuscripts of Leonardo da Vinci that he had 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 Mayic of Bishop Wilkins (1614-1672); the essential part of it is the water-screw of Archimedes, which appears in many of the earlier machines of this class. tSome 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 ; Papin, the well-known inventor of the digester, 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 w T ater in the wider part of the vessel weighing more will over balance 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 favourite field for
