The arms and legs should act alternately; the arms descending while the
legs are rising--(Plate XXII. fig. 3); and, oppositely, the arms rising
while the legs are descending. (Plate XXII. fig. 4.) Thus the action
of both is unceasingly interchanged; and, until great facility in this
interchange is effected, no one can swim smoothly, or keep the body in
one continued progressive motion. In practising the action of the legs,
one hand may rest on the top of a chair, while the opposite leg is
exercised. When both the arms and the legs are separately accustomed to
the action, the arm and leg of the same side may be exercised together.