[9] The upright and tapering arm of a catapult, with the iron pin on its top for the loop of the sling, is here fancifully likened to the erected tail of an angry scorpion with its sting protruding. FIG. 7.--CATAPULT (WITH A SLING), SEE OPPOSITE PAGE. A. The arm at rest, ready to be wound down by the rope attached to it and also to the wooden roller of the windlass. The stone may be seen in the sling. The upper end of the pulley rope is hitched by a metal slip-hook (fig. 6, p. 12) to a ring-bolt secured to the arm just below the sling. B. The position of the arm when fully wound down by means of the windlass and rope. See also EE, fig. 8, page 16. C. The position of the arm at the moment the stone D leaves the sling, which it does at an angle of about 45 degrees. E. By pulling the cord E the arm B is at once released from the slip-hook and, taking an upward sweep of 90 degrees, returns to its original position at A. [Illustration: THE SLING (OPEN).] [F. Its fixed end which passes through a hole near the top of the arm. G. The leather pocket for the stone. H. The loop which is hitched over the iron pin at the top of the arm when the stone is in position in the sling, as shown at A and B, fig. 7.] [Page 16] [Illustration: FIG. 8.--CATAPULT (WITH A SLING). Surface view of frame and mechanism. Scale: ½ in. = 1 foot. The arm EE is here shown wound down to its full extent. (Compare with B, fig. 7, page 14.)] I. I. } The side-pieces. II. II. } III. IV. The large cross-pieces. V. The small cross-piece. The ends of the cross-piece beams are stepped into the side-pieces. AA. The skein of twisted cord. BB. The large winding wheels. The skein is stretched between these wheels, its ends passing through the sides of the frame, and then through the wheels and over their cross-bars. (Fig. 12, p. 19.) By turning with a long spanner (fig. 6, p. 12) the squared ends of the spindles DD, the pinion wheels CC rotate the large wheels BB and cause the latter to twist the skein AA, between the halves of which the arm EE is placed. FF. The wooden roller which winds down the arm EE. (Fig. 6, p. 12.) The roller is revolved by four men (two on each side of the engine) who fit long spanners on the squared ends of the iron spindle GG. [Page 17] This spindle passes through the centre of the roller and through the sides of the frame. The small cogged wheels, with their checks, which are fitted to the ends of the spindle GG, prevent the roller from reversing as the arm is being wound down. (Fig. 6, p. 12.) HH. The hollows in the sides of the frame which receive the lower tenons of the two uprights. Between the tops of these uprights the cross-beam is fixed against which the arm of the catapult strikes when it is released. (Fig. 6, p. 12.)