Page:Popular Science Monthly Volume 90.djvu/561

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��of the great Jutland Battle has been fought out on this game-board.

On the board the home fleet is shown by light-colored ships, and the enemy's by dark-colored ones. When the game begins on the board the scouts are shown in contact. Behind their screen the supporting ships close up, and behind them the big battleships maneuver for the opening of fire action.

The war game as practiced now by all armies and navies w^as first devised by Von Moltke, who, when elevated to the post of Chief of Staff in 1857, introduced it into the German army. The United States army works out its problems on maps scaled twelve inches to the mile, at the Leavenworth Army School of the Line. The Coast Artillery has its own game, in which the advance of a hostile fleet is opposed by mines and gun fire. The artillerists are taught to identify at a glance every type of foreign vessel.


���Stopping the Automobile with a Vacuum Brake

AXEW brake has been invented for automobiles — a vacuum brake, which, as its name implies, operates not by the force of compressed air but by means of a vacuum created by the engine, operating rod. The mechanism of the new device consists of a cylinder containing a piston faced with leather, a lever that connects with the brake rod, a small controlling valve and sufficient copper tubing to connect the intake manifold with the valve and the vacuum cylinder.

When the engine is in operation a vacuum is created within the in- take manifold which amounts to a suction of about ten pounds to the square inch. This suction is employed to move for- ward the piston in the cylinder. By leverage this suction pull may be de- veloped to a thousand pounds pressure at the rear wheels. The pressure of a finger on a lever at the steer- ing post is sufficient to apply this tremendous force to the brakes.

��The vacuum brake with its thousand pounds pressure serves to counteract any inequality of brake adjustment. Thus if one brake requires three hundred pounds pressure to make it effective, while the other responds to not less than five hundred pounds pressure, it will be evident that one thousand pounds applied between them will be ample for both. This makes brake operation more certain and is an important safety factor.

The engine must be running in order to make the vacuum brake operative, but the ver>^ slowest movement of the motor is sufficient to get results. Even with the gear lever in neutral and the engine at rest, the application of the electric starter is sufficient, or the cranking of the engine by hand will accomplish the same result. A slight leak in the copper tubing will not interfere with the action of the vacuum brake.

W'hile acting as a service brake, this new "self-starter" is not designed to replace the hand or emergency brake which holds the car on a grade while the engine is idle. The cylinder is only four inches long and has a diameter of seven and three-eighths inches. It is braced in position by attaching it to cross members of the frame. The controlling valve may be attached to the lower part of the dash or the engine base.

��When the engine is in operation a vacuum is created within the intake manifold which amounts to a suction pull of ten pounds to the square inch. This is magnified by leverage

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