“The Carr Rock forms the seaward ledge of a range of sunken rocks, extending about two miles from Fifeness, on the eastern coast of Scotland, in North Latitude 56° 17’, and Longitude 2° 35´ west of London. By compass the Carr Rock Beacon bears SW. by W. from the Bell Rock, distant 11 miles; and from the Isle of May Light-house N.N.E. ¼ E., distant 6 miles. “The lower part of the beacon is a circular building of masonry, 18 feet in diameter, forming a basement for six pillars of cast-iron, terminating in a hollow ball of that metal, which measures 3 feet across, and is elevated about 25 feet above the medium level of the sea. “The erection of this beacon has been attended with much difficulty, having occupied six years in building; in the course of which the works sustained occasional damage. Mariners are therefore warned, when they _run_ for the Carr Rock Beacon, to do so with caution, both on account of its exposure to the breach of the sea, and its liability to receive damage from vessels under sail.” [Sidenote: Application of the tide-machine described.] The form and construction of the Carr Rock Beacon, both as originally intended, and ultimately executed, will be better understood by referring to Plate II., and to the annexed Description of the Plates. The motion to be given to the bell-apparatus, or tide-machine, was to be effected by admitting the sea water through a small aperture, of three inches in diameter, perforated in the solid masonry, communicating with a cylindrical chamber, in the centre of the building, measuring two feet in diameter, in which a float or metallic air-tank, was to rise and fall with the tide. The train of machinery for this apparatus was calculated for a perpendicular rise of only six feet, being equal to the lowest neap-tides on this coast. During the period of flood-tide, the air-vessel, in its elevation, by the pressure of the water, was to give motion to machinery for tolling the bell, and winding up a weight; which last, in its descent, during ebb-tide, was to continue the motion of the machine, until the flood-tide again returned to perform the joint operation of tolling the bell and raising the weight. A working model of a machine upon this principle having been constructed, it was kept in motion for a period equal to several months: this was effected by water run through a succession of tanks, raised by a pump from the lower one to the higher, thus producing the effect of flood and ebb tides. The time during which this apparatus was in action, having been ascertained by an index, a constant attendance upon the machine, during this protracted experiment, became unnecessary. [Sidenote: General application of tide-machinery.]