_The Balista._--This machine was used by the Romans for discharging the Falarica or ponderous spear, which had an iron head of over a foot in length at one end, with a ball of lead at the other end, and was at times used to carry incendiary material. It was projected upon the same principle as the stone in the catapult, namely by means of twisted skeins, but in the case of the balista two were in use. They were fitted vertically in a frame open to the front: an arm was passed through each skein, and when the skeins were twisted, the arms sought to diverge from one another. A rope acted like the string of a bow, and was wound back by a suitable apparatus, thus tending to draw the arms to a parallel position; upon its release the falarica was propelled in exactly the same manner as an arrow is discharged. It rested in a directing hollow trough until the trigger was pulled. These heavy missiles travelled at times to a distance of between three hundred and four hundred yards and it will thus be seen that practically the two ends of a bow are used for the propulsive force. The balista could also be used for discharging stones if required by a simple alteration of the bow-string, and the addition of another trough for directing the missile. _The Trebuchet._--The Trebuchet was a mediæval weapon derived from the classical engines of previous ages, but depending entirely upon the principle of the sling in contradistinction to that of torsion. It was a gigantic arm of wood, lengthened considerably by a sling; the arm was pivoted near one end remote from the sling, and this beam being actuated by the fall of an extremely heavy weight caused it to describe the quarter of a circle and discharge the missile. It superseded the catapult, chiefly for the reason that the making of the skeins of the latter had become a lost art, and also that a trebuchet could be quickly constructed on the spot required with materials generally found ready to hand, whereas the catapult necessarily had to be transported. Consequently trebuchets were invariably dismantled after a siege and not carried from place to place, the ponderous nature of the machine presenting an obstacle to such a course. There is no doubt that the addition of the sling was an idea obtained from the East at a very early date, as a MS. of the thirteenth century contains a representation showing it. In Add. MS. 10,292, British Museum, a trebuchet is shown in use against a castle which is being attacked by knights of the Ailette Period clad in banded mail. This shows the sling affixed to the arm, but no comparison of size is possible, as the machine is shown smaller than a horse, and the horse is nearly the size of the castle. In Roy. MS. 16, G. VI., dating from _c._ 1330, two trebuchets are shown in action against a castle. They are much out of drawing, as the arm bearing the counterpoise of one is actually shown longer than the arm bearing the sling, whereas it was probably only