Fig. 18. a Trainer or Rule, framed of timber, applied by the builders, for ascertaining the exact position of the stones of the respective courses. a is the eye or socket on which it was fitted to a steady-pin placed exactly in the centre. This rule was used chiefly for ascertaining the radiating direction of the stones, from the centre towards the circumference, being laid agreeably to corresponding notches and lines marked upon their upper-beds, so as to preserve band throughout the work, and prevent difficulty with the closing or finishing stones.
Fig. 19. is a perpendicular section of the carpenter’s jack, used with much advantage for shifting and turning the stones in the work-yard. The case of this machine was made of elm, and strongly bound at the ends with iron. It measured 4 feet in height, its greatest breadth 12 inches, and its thickness 6 inches. a a is the stock or case, b b the rack, fashioned at the lower end somewhat like the claws of a carpenter’s hammer. The upper end is of a forked form, both ends being conveniently applicable to the varied positions of the stones; c and d are the wheel and pinion work; e the handle by which the machinery is worked, affording a purchase or mechanical advantage in the ratio of about 64 to 1.
Fig. 20. is a plan of the useful machine called The Woolwich Sling-Cart, applicable to transporting large blocks of stone suspended between the wheels by means of a Lewis-batt. When a stone was of considerable length, it became necessary to employ a chain to steady it at the farther end, the application of which will be seen in this and the following figure. a a a a represent the shafts and body of the cart, b b b b the wheels, c c the handles passing between the spokes of the wheels, by which the machinery is worked for lifting the stone. The dotted line d d d d represents a plan of a stone in its state of suspension, e e e the wheel and pinion work, f the barrel or cylinder on which the chain turns as the stone is raised; g g is the tail-beam with its chain h h, and steady-pin i.
Fig. 21. represents the sling-cart in its working state, with letters corresponding to Fig. 20. Here the Bell Rock carter, and his horse, are shown, already noticed in the description of Plate VI., page [498].
Plate XI.
THE SHEER-CRANE, LEWIS-BATT, PRAAM-BOAT WITH CARGO, SLOOP SMEATON DISCHARGING, AND BRUCE’s TWO-HALF ATTENDING-BOAT.
Apparatus connected with the Bell Rock Works.
Drawn by G. C. Scott
Engd. by W. Miller.