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Et quos maliferæ despectant mœnia Abellæ

Teutonico ritu soliti torquere cateias. (Æn. vii. 740).

Jähn (p. 410)[116] remembers the Miölner, or hammer of Thor, which flew back to the hand.

Fig. 37.—Indian Boomerangs.

1. War Hatchet, Jibba Negros; 2. Steel Chakra, or Sikh Quoit; 3. Steel Collery; 4, 5. Collery of Madras, with knobbed handle.

Fig. 38.—Boomerang and Kite.

It has been noted that this peculiarity of reversion or back-flight is not generic, even in the true boomerang, but appertains only to specific forms. Doubtless it was produced by accident, and, when found useful for bringing down birds over rivers or marshes, it was retained by choosing branches with a suitable bend. The shapes greatly differ in weight and thickness, in curvature and section. Some are of the same breadth throughout; others bulge in the centre; while others are flat on one side and convex on the other. In most specimens the fore part of the lath is slightly ‘dished’: hence the bias causes it to rise in the air on the principle of a screw-propeller. The thin edge of the weapon is always opposed to the wind, meeting the least resistance. The axis of rotation, when parallel to itself, makes the missile ascend as long as the forward movement lasts, by the action of the atmosphere on the lower side. When the impulse ceases it falls by the line of least resistance, that is, in the direction of the edge which lies obliquely towards the thrower. In fact, it acts like a kite with a suddenly broken string, dropping for a short distance. But as long as the boomerang gyrates, which it does after the forward movement ends, it continues to revolve on the same inclined plane by which it ascended until it returns to whence it came. This action would also depend upon weight; the heavy weapons could not rise high in the air, and must drop by mere gravity before coming back to the thrower.