thickness or height, which is regulated by means of a gauge, known, in the technical language of the shed, as “_a grippers_” (fig. No. 21),[23] from its embracing the stone on three sides. It is simply a three-sided iron templet, having one long and one short tail (at right angles to the connecting piece), the space between the two tails shewing the thickness of the stone. [23] The figure shews “_a grippers_” for a stone 14 inches thick. [Illustration: No. 21.] The practical reader will readily see, that what has been said above about the hewing of granite, is chiefly applicable to the dressing of the large stones used in public works, such as docks, bridges, or marine towers; and it may be proper to add, that such heavy materials are always dressed on the ground, and that a piece of wood is placed under each end of the stone as a necessary precaution to prevent its being split by the blows of the mall. In dressing the lighter materials for house building, where a good deal of fine work is generally required, the stones are laid on what is called a _banker_, similar to that which is used in hewing freestone. The banker is a bench of stone 2¹⁄₂ or 3 feet long, and 2 feet broad, and is raised about 2 feet above the ground, so as to suit the workman’s convenience. In dressing one of the outside stones of the first or lowest courses of the Skerryvore Tower, a mason was occupied _eighty-five_ hours (see Plans of courses, Plate VIII.); and in dressing one of the largest of the hearting or inner stones of the same courses, _fifty-five_ hours. But as the work proceeded, owing to the greater readiness which the men had acquired in the application of the moulds, gauges and bevels, the time occupied, gradually decreased to the extent of about _ten hours_ for each stone, until the work had been carried on as far as to the thirteenth course, where the number of outside stones was reduced to twenty-four, at which stage of the work, the time required for dressing increased to about _one hundred and twenty hours_ for each outside stone. From that point upwards, the time again gradually decreased till we reached the sixty-fourth course, where it may be stated, that, on an average, a man was employed _sixty-three_ hours in dressing each stone; but the time gained in the last instance seemed to depend less on the readier application of the implements, than on the gradual diminution in the size of the stones, which, from that level upwards, decreased along with the thickness of the wall. But above the sixty-fourth course, a very marked increase in the time of dressing took place, owing to the introduction of the _ribband or ring joggles_ (shewn in the Plans of the 84th and 94th courses, Plate VIII.); and to the substitution of the _dovetailed joggles_ in the place of the _square_ or _diamond joggles_, which were used in the lower parts of the building. The time required for dressing a stone of the sixty-fifth course was _ninety-three_ hours of one man,