The least delay in doing this, and the resulting continuation of the immense strain on the arm, may cause it to fracture when it would not otherwise have done so.
The plans I have given are those of my largest engine, which, ponderous as it seems—(it weighs two tons)—is, however, less than half the size of the catapult used by the ancients for throwing stones of from forty to fifty pounds in weight.
As the plans are accurately drawn to scale, the engine can easily be reproduced in a smaller size.
An interesting model can be constructed that has an arm 3 feet in length, and a skein of cord about 4 inches in diameter. It can be worked by one man and will throw a stone, the size of an orange, to a range of 300 yards.
The sling, when suspended with the stone in position, should be one third the length of the arm, as shown in [fig. 7], p. 14.
If the sling is shortened, the ball will be thrown at a high elevation. If the sling is lengthened, the ball will travel at a lower angle and with much more velocity.
PART III
THE BALISTA
Fig. 13.—Balista For Discharging Heavy Arrows or Javelins.
Approximate scale: ½ in. = 1 foot.
This engine is here shown ready for discharge with its bow-string drawn to its full extent by the windlass.