The Mining Journal, of London, gravely publishes the following specification of a new motor, which, if it is a motor at all, is the long-sought for perpetual motion. The inventor says: In carrying out my invention I avail myself of the property of bodies or objects of a certain specific gravity when immersed in a fluid of a greater specific gravity to rise or ascend to the surface of such fluid; this buoyancy represents a greater or a lesser force or power, according to the greater or lesser difference between the specific graviiy of the obj ect and that of the fluid, and the size or the displacement caused in the fluid by such object. In order to make the said objects, which I will call floats, as light as possible, and yet strong; enough to resist the pressure of water, I construct them of thin sheet metal, and in preference in the form of tubes or hollow cylinders with conical or flat ends; a number or series of these cylinders are hinged or linked together in a similar manner as the buckets of a chain-pump ; this chain or float is passed over two sets of pulleys, disks, or arms fixed to two horizontal shalts, the one placed vertically above the other, the said pulleys being formed to suit the shape of the floats; one half of tliis chain of floats passes through the center of the tank holding the water or other fluid, and the other half passes outside the tank through the air. The floats when in motion enter through the bottom of the tank in the manner hereafter described, and rise up by their buoyancy through the water : they then pass round the top pulley, descend outside the tank and passing over the bottom pulley, again enter into the tank, and so on. Now, the principal part of my invention consists in passing the float through the bottom of the tank. On the bottom of the tank I fix a barrel or cylinder; this cylinder may be square or any suitable shape to fit one or more of the floats, and conical at one or both ends to admit of the free ingress and egress of the floats, and on every float I fix an ordinary cup leather, either made of leather, india-rubber, wood, metal, or any other suitable material. Supposing the floats to be in motion, the one float passing into the cylinder before the other has passed out would prevent very little if any escape of water, which escape could be pumped by a small pump into the tank again. The motion communicated by the rising floats to the float pulleys, disks, or arms and shaft is further transmitted by means of belts or gearing in the manner usual with othermotive engines. The details of arrangement and construction of my new motive-power engine may be altered or varied, but the main feature of my invention consists in passing the floats through the bottom of the tank. I do not confine myself to fixing the cup leathers, made either of leather, india-rubber, wood, metal, or any other suitable material, on the floats themselves, as I may in some cases fix the leathers, india-rubber, wood, metal, or any other suitable material in the barrel or cylinder at the bottom of tank, so as to form a water-tight joint round the floats passing through the cylinder or barrel. We should not have called our readers' attention to this had it not been that the same supposed principle in various modifications has been lately several times submitted to us, in the supposition that it would really give motive power. In one case the liquid employed was mercury, and in another it was oil, etc., but the idea in each was that continuous motion could be obtained by the action of buoyancy alone. Now what is buoyancy ? The ordinary definition of it fails to give a proper idea of the true reason why a body immersed in a fluid of greater specific gravity, rises to, and floats upon the surface. In short, the term is one of those inefficient ones still retained in scientific language. Let us suppose a U-shaped tube filled with water, the bend being at the bottom, and the tube stationary. The water will come to a common level in both legs of the tube. Now if we place a cork upon the surface of the liquid in one leg of the tube, the cork will, at first, sink a little, while the water in the other leg will rise a little and then remain at rest as before. Thus every vessel launched into the ocean raises the general level, while it sinks more or less into the water. If by means of a wire the cork be forced down below the surface of tho water the latter will rise in the opposite leg of the tube until its weight, in that leg, just equals the weight of the water and cork in the other leg, plus the weight of the wire or other force used to depress the cork. From this simple experiment it can be at once seen that floating of the cork is the result of the upward pressure of the liquid in which the cork is immersed ; which upward pressure is the result of an equal downward pressure in other portions of the liquid. Mechanics are too apt to read the enunciation of the law by which pressure is transmitted through liquids without appreciating its full forca Liquids transmit pressure equally in all directions. If buoyancy is the result of pressure it follows that no body or series of buoyant bodies can exert by virtue of their specific lightness an upward pressure greater, or as great as the weight of a mass of water equal to their aggregate bulk. To suppose they could exert an upward force equal to this bulk of water would be to suppose them destitute of weight. In the invention, the specification of which we have copied above, the pressure of the supernatant column of water upon the area of the aperture in the bottom of the tank through which it is proposed to pass the floats, will always be greater than the buoyancy of the floats, and instead of the floats being drawn successively in, through it, they would be effect ually prevented from entering. In short, neither mere pressure, nor buoyancy can, under any circumstances, produce motion, and the common mistake of the searchers after a perpetual motion is the non-appreciation of this fundamental fact. Pressure may indeed be converted into motion, but when his is done it is no longer pressure.