I, II. The side-pieces. These are each 10 ft. 6 in. long and 1 ft. thick. They are 21 in. high at their forward ends in front of the skein and are reduced to a height of 15 in. at their after ends behind the skein; see fig. 194, p. 282, for a side view of the catapult.

III. The after cross-piece. This is 15 in. high and 1 ft. thick.

IV. The forward cross-piece. This is 21 in. high and 1 ft. thick.

The cross-pieces (III, IV) are cut into tenons at their extremities and mortised into the side-pieces I, II.

V. The small cross-piece (6 in. square). This gives additional support to the sides of the catapult to enable it to resist the immense force of the skein of twisted cord.

The inside width between the sides of the catapult (I, II), when the cross-pieces (III, IV, V) are fixed, is 4 ft.

A, A. The skein of twisted cord.² The ends of the skein turn over the crossbars of the large wheels (B, B), which twist the skein. See figs. 197, 199, pp. 286, 293.

C, C. The pinion wheels which turn the large wheels, B, B.

By turning with long spanners the spindle heads (D, D), of the pinion

¹ In connection with this chapter and the next one, refer to Frontispiece for sketches of a catapult being used.

² The holes in the sides of the catapult - through which the skein of cord passes to the winches - are, of course, of the same diameter as the apertures inside the large wheels of the winches. See fig. 193, and II, fig. 197, p. 286.