On the flight of birds: turning by bending the tail
Why a bird curves its course, and the compound obliquity of wings and tail in flight
Headed "On birds," the page explains why a bird makes a revolving motion by bending its tail: a long body whose lateral extremities are equally distant from its central line moves straight, but if they are unequally distant its path curves through the air, the concave side lying toward the more remote extremity. A second section defines compound obliquity, when a bird flies holding its tail higher than its head and one wing lower than the other; such flight is always curved and is faster along the less oblique side, the curvature growing as the lateral obliquity decreases. Small marginal sketches show a bird in circular and in vertical descent.
On this page
Why a bird turns by bending its tail
All long bodies moving through the air whose lateral extremities are equally distant from the central line of their thickness move straight. But if those extremities are unequally distant, the body's path curves, and the curvature is concave on the side where the extremity is more remote from the central line.
Compound obliquity in the flight of birds
Compound obliquity is when a bird flies holding its tail higher than its head and one wing lower than the other. Such flight is always curved, is faster along the side that is less oblique, and its curvature grows greater as the lateral obliquity grows smaller.