short distance from the object to be raised. The opposite extremity then being forced down by the weight of one or more of the workmen, a force is applied to the object to be raised, bearing the same proportion to that applied to the lever, that the distance between the fulcrum and the extreme end of the lever does to that between the fulcrum and the object. Levers made of iron, and simply denominated "iron bars," are commonly used in raising and removing rocks. A machine called a "bed-screw" is frequently used for elevating buildings. It originally consisted principally of a large vertical screw, which was placed on a foundation called the "bed," and was turned by levers; but many improvements and variations have been added, till, in some instances, the screw has been dispensed with, and a rack and pinion have been substituted. Some of the best in use consist of a vertical iron rack, which is occasionally forced upward by the teeth of a pinion: a geer wheel on the same axle with the pinion being driven by the thread of a horizontal screw, to the head of which is attached a crank. By a machine of this construction, properly proportioned, one man may raise about twenty tons weight. Vertical screws, turned by levers, have been frequently used for the purpose of raising vessels to repair. But in these cases a large portion of the power applied is lost in the friction of the screw, and the process is laborious and tedious. This is probably the most awkward and injudicious method that has been applied to that purpose. Another method which has been applied to the purpose of elevating vessels, is decidedly ridiculous, although less laborious than the former. It is called the "hydraulic power," and consists in forcing water into large cylinders, by forcing pumps which are operated by steam power; while the water thus forced into the cylinder moves a piston and piston-rod, to which is connected several stout chains, which passing over corresponding pulleys, descend to a platform, on which rests the vessel to be raised. An expensive apparatus, called the "Marine Railway," constructed on the principle of the inclined plane, with a huge and complicated carriage to travel thereon, has been extensively used for taking vessels out of the water to repair. This plan is objectionable, however, on several accounts. It requires the application of a great quantity of power to overcome the friction of its many axles and machinery, in addition to what is requisite to overcome the gravity of the vessel. It is, moreover, injurious to the vessels which are taken up thereby, on account of its elevating the forward part, before the centre and stern become seated on the carriage. The most judicious mode in present use, for raising vessels to repair, and which must be preferred to all others, where there is a supply of water from an elevated reservoir, is on the principle of locks; the vessel being floated into one apartment, is elevated by the induction of water from above, till it can be floated over an elevated platform, where it is left at rest, while the water is allowed to pass off below. The sides of this upper box or apartment, are moveable, being attached to the bottom or platform by hinge joints, so that they may be let down to a horizontal position, thus giving the workmen the advantage of light and convenience. The "dry dock" in the Navy Yard at Charlestown, Mass., is constructed awkwardly enough; but as the vessels at that place are not raised, it does not come under this head. The massive stones which were used in the construction of some of the ancient edifices, were evidently raised by inclined planes. A huge mound of earth was built up round the building, completely enclosing it; and the elevation of the mound kept pace with that of the edifice: thus giving the laborers a chance to roll up the stones to their places. They used no other mechanical power than the simple windlass and lever; and no other carriage than a drag, under which was placed rollers. When the building was completed, the earth was taken away, and levelled about the vicinity. The modern method of raising stones for building, and which is now used in the building of heavy stone edifices, is by the use of a set of stout tackle blocks, the fall rope of which is taken up by a geered windlass, operated by a steam engine; the upper block being of course attached to an elevated shears or derick. Vessels, and other bodies, which have been sunk in the ocean, have been sometimes raised by means of airtight sacks, attached to different parts of the object by means of diving bells, been inflated with air, forced down through hollow tubes by pumps, till they thus acquired a buoyancy sufficient for the purpose. The power of buoyancy has also been applied for elevating vessels above water, by placing hollow trunks, filled with water, under the keel of the vessel, and then pumping them out. One of the best methods that has ever yet been proposed for raising vessels to repair, is to place under the keel a horizontal platform, to which is attached four large hollow trunks under its four corners: the trunks to be filled with water, and to have open apertures in the bottom of each. Then by allowing a stream of atmospheric air, to rush by its own expansive force from the reservoirs in which it had been previously compressed, through suitable pipes or hose, into each trunk, the water is expelled through the apertures in the bottom, and the vessel is elevated immediately, and without loss of time. In this case, the reservoirs (iron cylinders) of compressed air, may be recharged by steam or other power, during the process of repairing one vessel, and be thus in readiness for another. A patent has been granted for this invention, but it has not yet been put in operation on a scale of practical use, though the patentee would willingly give the right of the patent to any person or company who should be disposed to construct the apparatus on a large scale. We have recently given a description of Mr. Spencer's plan for elevating vessels, and some other modes have been recently projected, which we may describe in a future number.

Information to persons having business to
transact at the Patent Office.

Sec. 1. The existing laws relating to patents are those approved July 4, 1836, March 3, 1837, and March 3, 1839; all former acts having been repealed by the act of 1836.

Sec. 2. "Patents are granted for any new and useful art, machine, manufacture, or composition of matter, or any new and useful improvement on any art, machine, manufacture, or composition of matter, not known or used by others before his or their discovery or invention thereof, and not, at the time of his application for a patent, in public use, or on sale, with his or their consent, or allowance, as the inventor or discoverer." Act of 1836, section 6. "No patent shall be held to be invalid by reason of the purchase, sale, or use [of the invention,] prior to the application for a patent as aforesaid, except on proof of abandonment of such invention to the public, or that such purchase, sale or public use, has been for more than two years prior to such application for a patent."--Act of March 3, 1839.

Sec. 3. The term for which a patent is granted, is fourteen years; but it may, under certain circumstances, be renewed for seven years, as hereinafter mentioned.

Sec. 4. Patents are granted to citizens of the United States, to aliens who shall have been resident in the United States one year preceding, and shall have made oath of their intention to become citizens thereof, and also to foreigners who are inventors or discoverers.

Sec. 5. A patent may be taken out by the inventor in a foreign country, without affecting his right to a patent in the United States, provided the invention has not been introduced into public and common use in the United States prior to the application for such patent. In