The machine represented in the accompa ying engravings was invented by Ransom Cook, Esq., late Superintendent of the Clinton County State Prison, in the State of New York, and employed for the separation of the magnetic ore at the mines in that place. Our description of it is derived from the Scientific American. The principle of this invention consists in charging successively, by a battery, different rows of magnets on a revolving cylinder, so that the magnets shall lift magnetic ore from an endless web as it passes under the cylinder; and so also that when the ore is lifted up a short distance the electric connection shall be broken with the magnets, and the ore then drop from them into a trough, and be discharged into a proper receptacle.

Fig. 1, is a side elevation of the machine; fig. 2, a top plan; and fig. 3, a sectional view.

AA is the frame; B is a pulley, by which the cam-shaft, C, is revolved. This shaft by the cam, C, shakes the hopper, F, so as to spread the ore evenly across the web, H. This is done by having a hook rod that catches the upper edge of C, and is made, from the shape of the cam, to traverse across the web,

and spread the ore equally on the web. D is the revolving magnet cylinder, driven by band and pulleys, O, N. P. L is the trough into which the ore is discharged from the cylinder. XX are mercury troughs, the one charged positively, and the other negatively, from the battery, by the wires MM. The magnets are fixed on the revolving cyli der, and wound round with copper wire, the one positive and the other negative. These wires are carried from one magnet to another across the row, and brought out at the axle of the cylinder, to form a circular fan row of the points of the wires, so that as the cylinder revolves, and these wires dip into the charged mercury troughs, the rows of magnets are charged and broken alternately, to lift the ore from the dross, and deposit it in the receiving trough.

K is the hook shaft or bar which is made to shake the hopper, F, as already described. H is the endless web or apron carrying the ore forward to the magnets on the cylinder, D. The magnetic cylinder revolves to meet the ore as it comes forward on the web, and not in a contrary direction, as might be inferred. TT are the magnets. M represents the

wires from the battery. The large cylinder is revolved by a broad band from the other side passing over a large pulley on the shaft of D, the magnetic cylinder. E represents the copper wires that are wound around the magnets, showing the manner in which they are formed on the outside of the axle, so as to dip into the charged mercury troughs and be charged. As they rise out of the troughs, the electric current is broken and the magnets discharged. As the cylinder is made of wood, it is non-conducting, and to keep the wires from the axle of the cylinder, it (the axle) is boxed up with wood and wires turned up on the outside of it.

Fig. 3 shows the manner in which the magnets are arranged on the cylinder. D, is the cylinder; TT, the magnets; E, the current wires; and X, the trough or vessel of quicksilver. The cylinder is about 30 inches in diameter, and the magnets are about five-eighths of an inch thick with four polar points, the negative and the positive on each magnet. There is a space of about three-fourths of an inch between each of the magnets, and a large one has had ten magnets in a row with thirty rows on the cylinder. It will be observed that the wires are alternately wound in the direction of the polar currents. One wire is now represented as dipping in the mercury, but one-fourth of all the magnets are charged at the same time, as that number touch the mercury on the under side of the cylinder; but the magnets are charged and discharged successively in rows. The ore is carried forward on the endless apron ; and the magnet cylinder, by revolving in the same direction as the apron, lifts the ore, while the dross is discharged from the apron while passing over the roller.

This machine is not an untried one. It has been fairly tested, having been in operation at Plattsburg for some time, where it is stated to have exceeded the most sanguine expectations. When ore is associated with hornblende, no other process of separation can it appears compare with this.

ON FLAMBING THE BOWS OF SHIPS.-IN ANSWER TO "F." ("MECH. MAG.," NO. 1349.)

Mr. Editor,--Almost in every sailing vessel, and certainly in all vessels car

rying goods, the weight of displacement at some distance from the stem is less than the weight of hull and lading, &c., included in the same part of the ship. This deficiency of buoyancy at the extremities cannot be obviated, except by adopting an entirely different plan of construction in our men-of-war; but we should not increase the evils attendant on the same, when as yet no better plan of carrying the armament in the bows has been practically carried out.

This want of displacement for those necessary weights which, in every class of men-of-war are fixed to an almost unalterable distance from the stem, "F." has not, apparently, taken into account, as appears from his conclusions. "F." begins his conclusions as follows:

"Because the displacement or weight of the section of A before a is very much greater than the similar one before b in B, its momentum will be greater."

Now, the displacement of A before a cannot very properly be substituted for the weight of the section before a, these two quantities being, as said above, never equal.

"F's" next remark is—

"Because the displacement of A before a is greater than that before b in B, so A will lose more buoyancy by the passage of the wave aft than B, and a will require to fall further than B before the equalisation of weight and buoyancy is restored."

The displacement of A will certainly lose more buoyancy than B by the passage of the wave behind; but it can also afford to lose more than B, being less deficient in buoyancy for the weights it has to carry than the form B; and although the bow A will rise higher on the crest of the wave, it will never fall so deep in the hollow of the wave as that of B. First, at the moment when the weights in the bow plunging in the hollow of the passing wave are supported by an equal weight of water, the falling ceases, and this moment must arrive earlier in A than in B; the water will embrace the bow, B, an inch nearer to the deck than the full bow, A, which possesses a greater fullness at and above the water line.

It may be well to state that I am neither an advocate for an overhanging bow, nor for an excessive full forebody