Our previous illustration of a break by the Knox system was its simplest and best appli cation. An identical case would be one where a large and loose block of stone was split up into smaller ones by one or more Knox holes. But those who use this system do not confine it to such cases alone. Horizontal holes are frequently put in, and artificial beds wade by " lofting." In such eases, where the rock has a rift " parallel with the bed, one hole about half way through is sufficient for a block about 15 ft. square, but in " liver" rock the holes must be drilled nearly through the block, and the size of the block first reduced. A more difficult application of the Knox system, and one requiring greater care in its successful use, is where the block of stone is situated as in the case hereinbefore cited, except that both ends are not free, one of them being solidly fixed in the quarry wall. A simple illustration of a case of this kind is a stone step on a stairway which leads up and along a wall. Each step has one end fixed to the wall and the other free. Each step is also free on top, on the bot tom. and on the face, but fixed at the back. We now put a Knox hole in the corner, at the junction of the step mid the wall. The shape of the Knox hole is as shown in Fig. 17.
It is here seen that the grooves arc at right angles with each other, and the block of stone is sheared by a break made opposite the bench, as in the previous case, and an addi tional break made at right angles. and at the fixed end of the block. Sometimes a corner break is made by putting in two of the regular straight Knox holes in the lines of the pro posed break, and without the use of the corner hole.
ItAILIWAD, CABLE. The wire-cable system of street railways was first put into use in San Francisco, Cal., in 1873, when the Clay Street Hill Railroad was constructed in ac cordance with the plans of Mr. Andrew S. Practical employment has proved that the system possesses, among others, advantages which may be summa rized as follows: The steepest grades are as easily worked as levels ; the cars may be stopped instantly at any point on the line, and started with promptness and ease ; the speed is uniform, and any rate may be estab lished that is desired ; the method of working is noiseless and even ; cleanliness of the track is secured ; a capacity of increase is obtainable at any time an increased carrying capacity may he required, and there is freedom from snow blockade.
The Cable System of the P«eifie and A'ational Railway Companies is based upon the patents of Hallidie, llovey, Paine, Root, and others, and is now employed in San Francisco, Chicago, St. Louis, and many other cities, and also on the East River Bridge, between New York and Brooklyn. It, consists simply of an endless wire rope placed in a tube a narrow slot from 4 to .1 in. wide), beneath the surface and between the rails, maintained in its position by means of sheaves,wheels, or rollers. The rope is kept con tinuously in motion by a stationary steam-engine at either end of the line, or at any convenient point be tween the twoextremes. A gripping attachment at the end of a vertical steel rod connected with the Or, and passing through the narrow slot in the tube, transmits the mo tion of the cable to the car. The speed at which the car moves is de termined by the rapidity of the cable, and this is regulated by the revolutions of the driving-wheel at the stationary engine. The cable is grasped and released at pleasure, and the movement of the ear controlled by one man. The car or cars (there may be any number used together)
start without shock or jar, and are stopped instantly at any point more readily than a horse car, and hence are less liable to accidents. The system can be adapted to any grade or curvature, even to turning the corner of a street at acute angles of limited radius. A variety of different forms of gripping attachmentsor '• grips " have been devised. The typical variety used on the Clay Street Rill Railroad is illustrated in Figs. 1 and 2. A vertical slide, Fig. 1, works in a shank, and is moved up and down by a screw and hand-wheel. The small upper screw going down through the large hollow screw operates it. At the lower end of this slide is a wedge-shaped block. The wedge actuates two jaws horizontally, which open and close according to the direction in which the slide is moved, closing when the slide is moved upward. These jaws have pieces of soft east-iron placed in them, which are easily removed when worn out. These pieces of iron arc of proper shape and size inside to grip the rope when they are closed over it. On both sides of these jaws and attached to them are four small pulleys. These pulleys are held by means of rubber cushions, sufficiently in advance of the jaws to keep the rope off from the jaws and at the same time to lead the rope fairly between them, allowing it to travel freely between the jaws when they are separated, without touching them. When it is required to grip the rope, this slide is drawn up by means of the small screw and hand wheel, before described, and the wedge at the lower end closes the jaws over the rope, at the same time forcing back the small guide sheaves onto the rubber cushions. The shank, containing the slide, etc., is enclosed and retained in cast-iron slides attached to the body of the car, and a wrought-iron standard, having a large nut at its upper end, in which the large hollow screw works, The grip is raised and lowered bodily through the opening in the tube from above the surface of the street to the rope in the tube by means of the hand-wheel and nut working on the large hollow screw referred to. The grip is secured to a skeleton or trac tion-car called a dummy. The dummy is coupled to the passenger cars at the bottom of the incline and uncoupled at the top, and vies verse. At first the connection between the dummy and car was made by means of spiral springs, to prevent, any jar in starting up ; but this was soon found unnecessary. The arrangements made at the bottom of the incline for keeping the rope at the proper tension, and taking up the slack, prevent any noticeable jar in starting. As before stated, the rope is constantly in motion, running between sheaves placed in the tube. The slot of the tube is on one side of a vertical line drawn through the center of the tube and referring to Fig. 3 it will be seen that the foot of the gripping attachment projects on one side, giving it an L-shape, enabling tire jaws to pass under and over the rope sheaves in tube. In order to stop the car, the jaws of the grip ping attachment are slightly opened ; when they release the rope the guide sheaves take it, and the car stops. In another form of grip used on the Sutter Street Railroad, San Francisco, the motion of the grip ping jaws is vertical, instead of horizontal, and the rope is taken up and released at the side. In order to run upon or off the rope at the termini of the road, the track and slot diverge from or converge to the line of tire rope. Levers are used for operating the jaws instead of the screw.