The overhand movement enables the swimmer to throw himself forward on the water, and to move his arms and legs in a nearly vertical instead of a horizontal plane; the extremities working, as it were, above and beneath the trunk, rather than on either side of it. The extremities are consequently employed in the best manner possible for developing their power and reducing the friction to forward motion caused by their action. This arrangement greatly increases the length of the effective stroke, both of the arms and legs, this being equal to nearly half an ellipse. Thus when the left arm and leg are thrust forward, the arm describes the curve _a b_ (fig. 42), the leg _e_ describing a similar curve. As the right side of the body virtually recedes when the left side advances, the right arm describes the curve _c d_, while the left arm is describing the curve _a b_; the right leg _f_ describing a curve the opposite of that described by _e_ (compare arrows). The advancing of the right and left sides of the body alternately, in a nearly straight line, greatly contributes to continuity of motion, the impulse being applied now to the right side and now to the left, and the limbs being disposed and worked in such a manner as in a great measure to reduce friction and prevent dead points or halts. When the left arm and leg are being thrust forward (_a b_, _e_ of fig. 42), the right arm and leg strike very nearly directly backward (_c d_, _f_ of fig. 42). The right arm and leg, and the resistance which they experience from the water consequently form a _point d’appui_ for the left arm and leg; the two sides of the body twisting and screwing upon a moveable fulcrum (the water)--an arrangement which secures a maximum of propulsion with a minimum of resistance and a minimum of slip. The propulsive power is increased by the concave surfaces of the hands and feet being directed backwards during the back stroke, and by the arms being made to throw their back water in a slightly outward direction, so as not to impede the advance of the legs. The overhand method of swimming is the most expeditious yet discovered, but it is fatiguing, and can only be indulged in for short distances. [Illustration: FIG. 43.--Side-stroke Swimming.--_Original._]