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An illustration of an "elastic spiral wing, which twists and untwists during its action, to for a mobile helix or screw. This wing is made to vibrate by a direct piston action, and b a slight adjustment can be propelled vertically, horizontally or at any degree of obliquity." -Britannica, 1910

Elastic Spiral Wing

An illustration of an "elastic spiral wing, which twists and untwists during its action, to for a mobile…

An illustration of a double elastic spiral wing.

Double Elastic Spiral Wing

An illustration of a double elastic spiral wing.

An illustration of elastic spiral wings of the gull. "a b, Anterior margin of the left wing; c d, Posterior margin of the ditto; d g, Primary or rowing feathers of left wing; g a, Secondary feathers ditto; x, root of right wing with ball-and-socket joint; l, Elbow joint; m, Wrist joint; n o, Hand and finger joints." -Britannica, 1910

Elastic Spiral Wings of the Gull

An illustration of elastic spiral wings of the gull. "a b, Anterior margin of the left wing; c d, Posterior…