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