Why is it physically advantageous to turn out the toes?

Because the supporting base of a man consists of the feet and the space between them; and turning out the toes, without taking much from the length of the base, adds a good deal to the breadth.-Arnott.

Why do very fat people usually throw back their head and shoulders?

Because, by so doing, they keep the centre of gravity of the body over the base.

SIMPLE MACHINES.

Why have the "simple machines," as the lever, wheel and axle, plane, wedge, screw, and pulley, been long called the "mechanic powers?"

Because they were first used to raise great weights, or overcome great resistances. Hence the common error in supposing that they generate force, or have a sort of innate power for saving labour; whereas, neither simple machines nor mechanic powers save labour, in a strict sense of the phrase.

Why, then, are these machines advantageous?

Because they allow a small force to take its time to produce any requisite magnitude of effect. Thus, one man's effort, or any small power, which is always at command, by working proportionally longer, will answer the purpose of the sudden effort of many men, even of hundreds or thousands, whom it might be most inconvenient and expensive, or even impossible to bring together.

Why are there so many vain schemes for perpetual motions, and new mechanical engines of power?

Because the projectors do not understand the great truth, that no form or combination of machinery ever did or ever can increase, in the slighest degree, the quantity of power applied. Hence the futility of supposing that a lever, or great pendulum, or spring, or

schemes for perpetual nes of power? understand the great on of machinery ever e slighest degree, the ence the futility of supendulum, or spring, or

heavy fly-wheel, &c. can ever exert more force than has passed into it from some source of motion.-Arnott.

THE LEVER.

Why is a beam or rod of any kind, resting at one part on a prop or axis, which becomes its centre of motion, a dever?

Because such a contrivance was first employed to lift (levare, Latin) weights.

The lever, in mechanics, compensates power by space, and what is lost in power is gained in time. If the lever be 17 feet long, and the pivot or fulcrum be a foot from one end, an ounce placed on the other end will balance a pound placed on the near end. If, instead of an ounce, we place upon the long end the short end of a second beam or lever, supported by a fulcrum one foot from it, and then place the long end of this second lever upon the short end of a third lever, whose fulcrum is one foot from it; and if we put upon the end of this third lever's long arm an ounce weight, that ounce will move upwards a pound on the second lever's long arm;/and this moving upwards, will cause the short end to force downwards 16 pounds at the long end of the first lever, which will make the short end of the first lever move upwards, although 256 pounds be laid upon it. The same effect continuing, a pound on the long end of the third lever, will move up a ton and three-quarters at the short end of the first lever, so that the touch of a child's finger, will move as much as two horses can draw.-Notes in Science. "Give

Why did Archimedes reasonably enough say, me a lever long enough, and a prop strong enough, and with my own weight I will move the world?"

Because there is no limit to the difference of intensity in forces, which may be placed in opposition to each other by the lever, except the length and strength of the material of which the levers must be formed. But he would have required to move with the velocity

of a cannon-ball for millions of ages, to alter the position of the earth by the small part of an inch. This feat of Archimedes is, in mathematical truth, performed by every man who leaps from the ground, for he kicks the world away when he rises, and attracts it again when he falls back.-Arnott.

Why is a finger caught near the hinge of a shutting door so much injured?

Because the centre of action of the door moves through a space comparatively great, and acts with a great lever-advantage on a resistance placed near the fulcrum of the lever where there is little motion. Children pinching their fingers in this way, or in the hinge of the fire-tongs, where there is a similar action, wonder why the bite is so keen.

Why have pincers or forceps such extraordinary power?

Because they are double levers, of which the hinge is the common prop or fulcrum. Dr. Arnott thus illustrates the advantages of this machine :-In drawing a nail with steel nippers, we have a good example of the advantages of using a tool; 1. The nail is seized by teeth of steel, instead of by the soft fingers; 2. Instead of the griping force of the extreme fingers only, there is the force of the whole hand conveyed through the handles of the nippers; 3. The force is rendered, perhaps, six times more effective by the lever length of the handles; and, 4. By making the nippers, in drawing the nail, rest on one shoulder as a fulcrum, it acquires all the advantages of the lever or claw-hammer for the same purpose.

Why do lofty sails often cause open boats to upset?

Because the mast and sails set upon it are as a long lever, having the sails as the power, turning upon the centre of buoyancy of the vessel as the fulcrum, and lifting the balance or centre of gravity as the resist