Double March.--On the word Double March, the whole step off together with the left feet, keeping the head erect, and the shoulders square to the front; the knees are a little bent; the body is more advanced than in the other marches; the arms hang with ease down the outside of the thighs. The person marching is carefully habituated to the full pace of thirty-six inches, otherwise he gets into the habit of a short trot, which defeats the obvious advantages of this degree of march. In the army, great advantage attends the constant use of the plummet; and the several lengths swinging the times of the different marches in a minute, are as follow:-- In. Hun. Slow time 75 steps in the minute 24,96 Quick time 108 „ „ 12,03 Double march 150 „ „ 6,26 A musket ball, suspended by a string which is not subject to stretch, and on which are marked the different required lengths, answers the above purpose, may be easily acquired, and is directed to be frequently compared with an accurate standard in the adjutant’s possession. The length of the plummet is to be measured from the point of suspension to the centre of the ball. In practising all these paces, the pupils should also be accustomed to march upon a narrow plane, where there is room for only one foot, upon rough uneven ground, and on soft ground which yields to the foot. Walking exercises a greater influence over the economy when it takes place on inclined planes than on a flat surface. In ascending, the effort is made in a direction directly opposed to the general tendency of heavy bodies: the body is strongly bent, the upper part of the trunk in advance; the action of the posterior and anterior muscles of the thigh is considerable; and circulation and respiration are speedily accelerated by the violence of the muscular contractions. In descending, on the contrary, effort is requisite to keep up the body, which tends to obey the laws of gravitation; and to moderate the tendency of gravity to project forward in the centre, the body is thrown back, the sacro-spinal mass, and the posterior muscles of the neck, are strongly contracted, the knees bent, and the steps much shorter. Men with long flat feet, and the heel bone little projecting, are bad walkers. FEATS IN WALKING. The power of walking great distances without fatigue is an important matter, in which the English have of late excelled. A good walker will do six miles an hour, for one hour, on a good road.[3] If in perfect training, he may even do twelve miles in two hours. Eighteen miles in three hours is a much more doubtful affair, though some are said to have achieved it. [3] Seven miles in one hour are said to have been done by some.