Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/581

 P E R P E R 555 the vain quest ; for, if by capillary 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, arid thus perpetual 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 Wil liam Congreve, who invented the rockets that bear his name. EFG (fig. 3) is an inclined plane over pulleys ; at the top and bot tom 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; there fore the extra weight of ab will cause the chain to move round in the direction of the arrow, and this will go on continually, The more recondite vehicles of energy, such as electricity and magnetism, are more seldom drawn upon by perpetual- motion inventors than might perhaps be expected. In stances do occur, but devices of this kind have not become a common part of the folklore of nations like the over balancing wheel and the self-sufficient water-mill. Gilbert, in his treatise De Magnete, alludes to some of them, and Bishop Wilkins mentions among others a machine &quot;wherein a loadstone is so disposed 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.&quot; The fact that screens do exist whereby elec trical and magnetic action can be cut off would seem to open a door for the perpetual -motion seeker. Unfortu nately the bringing up and removing of these screens involves in all cases just that gain or loss of work which is demanded by the inexorable law of the conservation of energy. A shoemaker of Linlithgow called Spence pre tended that he had found a black substance which inter cepted 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 Brewster thought the thing worth mentioning in a letter to the Annales de Ckimie, 1818, wherein he states &quot;that Mr Playfair and Captain Kater have inspected both of these machines and are satisfied that they resolve the problem of perpetual motion.&quot; Not very long ago the writer of this article received by post an elaborate drawing of a locomotive engine which was to be vorked by the agency of permanent magnets. He forgets the details, but it was not so simple as the plan represented in fig. 4, where M and N are permanent magnets, whose attraction is &quot; screened &quot; by the wooden blocks A and B from the upper left and lower right quad rants of the soft iron wheel W, which consequently is attracted round in the same direction by both M and N, and thus goes on for ever. One more page from this chapter of the book of human folly ; the author is the famous John Bernoulli. We translate his Latin, as far as possible, into modern phraseo logy. In the first place we must premise the following (see fig. 5). 1. 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. Wherefore, 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. Construction. These things being presupposed, I thus construct a perpetual motion. Let there be taken in any (if you please, in equal) quantities two liquids of different densities mixed together (which may be had by Hyp. 4), and let the rntio of their densities be first determined, and be the heavier to the lighter as G to L, then with the mixture let the vase AD be filled up to A. This done, let the tube EF, open at both ends, be taken of such a length that AC:EF&amp;gt;2L:G+L; let the lower orifice F of this tube In stopped, or rather covered with the filter or other material separating the lighter liquid from the heavier (which may also be had by Hyp. 5) ; now let the tube thus prepared be immersed to the bottom of the ves sel CD ; I say that the liquid will continually ascend through the ori- &quot;g^^s^ (ice F of the tube and overflow by the orifice E upon the liquid below. Q Demonstration. Because the ori fice F of the tube is covered by the L ~ ~ filter (by constr. ) which separates the lighter liquid from the heavier, it follows that, if the tube be immersed to the bottom of the vessel, the lighter liquid alone which is mixed with the heavier ought to rise through the filter into the tube, and that, too, higher than the surface of the surrounding liquid (by Hyp. 2), so that AC : EF = 2L : G + L ; but since (by constr.) AC: EF&amp;gt;2L:G + L it necessarily follows (by Hyp. 3) that the lighter liquid will flow over by the orifice E into the vessel below, and there will meet the heavier and be again mixed with it ; and it will then penetrate the filter, again ascend the tube, and be a second time driven through the upper orifice. Thus, therefore, will the flow be continued for ever. Q.E.D. He then proceeds to apply this theory to explain the perpetual rise of water to the mountains, and its flow in rivers to the sea, which others had falsely attributed to capillary action, his idea being that it was an effect of the different densities of salt and fresh water. One really is at a loss with Bernoulli s wonderful theory, whether to admire most the conscientious statement of the hypothesis, the prim logic of the demonstration, so care fully cut according to the pattern of the ancients, or the weighty superstructure built on so frail a foundation. Most of our perpetual motions were clearly the result of too little learning ; surely this one was the product of too much. (G. CH.) PERPIGNAN (Spanish, Perpinan), the ancient capital of Eoussillon, and now the chief town of the department of Pyrenees Orientales, France, and a first-class fortress,