[6] _The Crossbow_, _etc._ If the upper end of the arm of a catapult is shaped into a cup to receive the stone, as shown in fig. 5, p. 11, the arm is, of necessity, large and heavy at this part. If, on the other hand, the arm is equipped with a sling, as shown in fig. 6, opposite page, it can be tapered from its butt-end upwards, and is then much lighter and recoils with far more speed than an arm that has an enlarged extremity for holding its missile. When the arm is fitted with a sling, it is practically lengthened by as much as the length of the sling attached to it, and this, too, without any appreciable increase in its weight. The longer the arm of a catapult, the longer is its sweep through the air, and thus the farther will it cast its projectile, provided it is not of undue weight. The difference in this respect is as between the range of a short sling and that of a long one, when both are used by a school-boy for slinging pebbles. The increase of power conferred by the addition of a sling to the arm of a catapult is surprising. A small model I constructed for throwing a stone ball, one pound in weight, will attain a distance of 200 yards when used with an arm that has a cup for holding the ball, though when a sling is fitted to the arm the range of the engine is at once increased to 300 yards. The only historian who distinctly tells us that the catapult of the Greeks and Romans had a sling to its arm, is Ammianus Marcellinus. This author flourished about 380 A.D., and a closer study of his writings, and of those of his contemporaries, led me to carry out experiments with catapults and balistas which I had not contemplated when my work dealing with the projectile engines of the Ancients was published. [Page 14] [Illustration: FIG. 7.--CATAPULT (WITH A SLING). Side view of frame and mechanism. Scale: ½ in. = 1 ft.] [Page 15] Ammianus writes of the catapult[7]: ‘In the middle of the ropes[8] rises a wooden arm like a chariot pole ... to the top of the arm hangs a sling ... when battle is commenced a round stone is set in the sling ... four soldiers on each side of the engine wind the arm down till it is almost level with the ground ... when the arm is set free it springs up and hurls forth from its sling the stone, which is certain to crush whatever it strikes. This engine was formerly called the “scorpion,” because it has its sting erect,[9] but later ages have given it the name of Onager, or wild ass, for when wild asses are chased they kick the stones behind them.’ [7] _Roman History_, Book XXIII., Chapter IV. [8] _i.e._ in the middle of the twisted skein formed of ropes of sinew or hair.