nate with the vertical joints of the courses above and below it, or, as it is termed, break joints with them, is the most simple, and offers, in most cases, all requisite solidity. In this

system (Fig. 20), the blocks of each course are laid alternately with their greatest and least dimensions to the face of the wall; those which present the longest dimension along the face are termed stretchers; the others, headers. If the

header reaches from the face to the back of the wall, it is termed a through; if it only reaches part of the distance it is termed a binder. The vertical joints of one course are either just over the middle of the blocks of the next course below, or else, at least four inches on one side or the other of the vertical joints of that course; and the headers of one course rest as nearly as practicable on the middle of the

stretchers of the course beneath. If the backing is of rubble, and the facing of cut stone, a system of throughs or binders, similar to what has just been explained, must be used.

By the arrangement here described, the facing and backing of each course are well connected; and, if any unequal settling takes place, the vertical joints cannot open, as would be the case were they in a continued line from the top to the bottom of the mass; as each block of one course confines the ends of the two blocks on which it rests in the course beneath.

392. In masses of cut stone exposed to violent shocks, as those of which light-houses, and sea-walls in very exposed positions are formed, the blocks of each course require to be not only very firmly united with each other, but also with the courses above and below them. To effect this, various means have been used. The beds of one course are sometimes arranged with projections (Fig. 21) which fit into corresponding indentations of the next course. Iron cramps in the form of the letter S, or in any other shape that will answer the

A

B

D

an

Fig. 21-Represents elevation, A, plan, B, and perspective views, C and D, of two of the blocks of a wall in which the blocks are fitted with indents, and connected with bolts and cramps of metal.

purpose of giving them a firm hold on the blocks, are let into the top of two blocks of the same course at a vertical joint, and are firmly set with melted lead, or with bolts, so as to confine the two blocks together. Holes are, in some cases, drilled through several courses, and the blocks of these courses are connected by strong iron bolts fitted to the holes.

The most noted examples of these methods of strengthening the bond of cut stone, are to be found in the works of the Romans which have been preserved to our time, and in two celebrated modern structures, the Eddy-stone and Bell-rock light-houses in Great Britain (Fig. 22).

Fig. 22-Represents the manner of arranging stones of the same course by dove-tail joints and joggling, taken from a horizontal section of the masonry of the Bellrock light-house.

Figs. 23, 24, 25, 26.-Plans and sections showing the masonry bond and metal fastenings of some of the courses in the Minot's ledge light-house.

Fig. 23.-Rock surface prepared for receiving foundation.

393. The manner of dressing stone belongs to the stonecutter's art, but the engineer should not be inattentive either to the accuracy with which the dressing is performed, or the means employed to effect it. The tools chiefly used by the workman are the chisel, axe, and hammer for knotting. The usual manner of dressing a surface is to cut draughts around and across the stone with the chisel, and then to use the chisel,

the axe with a serrated edge, or the knotting hammer, to work down the intermediate portions into the same surface with the draughts. In performing this last operation, the chisel and

Fig. 26-Vertical section and interior elevation above foundation courses.

axe should alone be used for soft stones, as the grooves on the surface of the hammer are liable to become choked by a soft

material, and the stone may in consequence be materially injured by the repeated blows of the workman. In hard stones this need not be apprehended.

In large blocks which require to be raised by machinery, a hole, of the shape of an inverted truncated wedge, is cut to

P

Fig. 27-Represents a perspective
view, A, of a block of stone with
draughts around the edges of its
faces, and the intermediate space
axed, or knotted, and its tackling
for hoisting: also the common
iron lewis, B, with its tackling.
a, draughts around edge of block.
b, knotted part between draughts.
c, iron bolts with eyes let into oblique
holes cut in the block.

d and e, chain and rope tackling.
n, n, side pieces of the lewis.

Bo, centre piece of lewis with eye fast

ened to n n by a bolt.

p, iron ring for attaching tackling.

receive a small iron instrument termed a lewis (Fig. 27), to which the rope is attached for suspending the block; or else, two holes are cut obliquely into the block to receive bolts with eyes for the same purpose.

When a block of cut stone is to be laid, the first point to be attended to is to examine the dressing, which is done by placing the block on its bed, and seeing that the joints fit close, and the face is in its proper plane. If it be found that the fit is not accurate, the inaccuracies are marked and the requisite changes made. The bed of the course on which the block is to be laid is then thoroughly cleansed from dust, &c., and well moistened, a bed of thin mortar is laid evenly over it, and the block, the lower surface of which is first cleansed and moistened, is laid on the mortar-bed, and well settled by striking it with a wooden mallet. When the block is laid against another of the same course, the joint between them is prepared with mortar in the same manner as the bed.