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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1873 Excerpt: ... stability may be cited. A pyramid owes its great firmness to the breadth of its base and the low position of the centre of gravity. Walls are often strengthened with small expenditure of material by building offsets or by battering the side toward which the forces tending to overturn them are directed. A high carriage is upset much more readily than a low one, because the centre of gravity is higher, so that a smaller horizontal force overcomes its dynamical stability, and also if the road is sloping a less inclination is required to throw the line of direction outside of the base. For this reason wagons intended for carrying heavy loads are generally made so as to have the greater part of the load lower than the axles of the wheels. Quadrupeds have a much greater stability than man, because of the broader base formed by their feet, hence their young acquire the art of walking far more rapidly than a child, which must first learn the art of balancing itself on its legs. The human figure is most stable when the feet are so "placed as to make the base as large as possible. If the heels are in contact this occurs when the angle of the feet is 90. If the heels are separated by an amount equal to the length of the foot, their angle should be 60. CHAPTER X. Mechanical Powers. 173» D3.fi.altIon-The forces subject to our use can be applied only by means of machinery of greater or less complexity. Machines are either simple or compound. The elementary machines to which all systems may be reduced are called the mechanical powers. They are seven in number, viz.:--the lever, wheel and axle, cord, pulley, inclined plane, wedge, and screw. These may again, in principle, be reduced to three, the lever, cord and inclined plane, the first of these comprehending t...
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