Page:Popular Science Monthly Volume 91.djvu/630

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��Popular Science Monthly

��Blackboard an Adjunct to the Amateur's Shop

A BLACKBOARD is a valuable adjunct to the amateur's shop. One may easily be made of a sheet of cardboard painted with a mixture of lampblack and gasoline and then tacked in a convenient place on the shop wall with crayon box nearby. — Harold W. Offius.

��A Grid Placed in the Wings of an Airplane

IN wireless telegraph work on airplanes there is often difficulty encountered in obtaining sufficient metal work to serve in a balancing capacity.

In the construction the bracing wires of the wings are so connected that they provide a good path throughout the whole length of the wing, through which they are led to the wireless transmitter. To prevent air friction, additional wires are mounted inside the wing frames which are connected with the bracing wires. These wires are supported by lashings through the slots in

���Wires making the grid for an aerial are placed in the frame of an airplane wing

the ribs. As these wires form a grid they are placed parallel and are of equal lengths. In the illustration the bracing wires are shown at A. They may be either bare or insulated. At B is a modification of a grid, the wires being supported by lashings through slots in the ribs.

��A Simple and Interesting Thermo- Magnetic Motor

AVERY simple thermo-magnetic motor which utilizes the principle that heat- ing a piece of metal weakens its magnetic properties, can be easily built. The rim of

��Magnet

���The wheel rim is heated by a lamp to reduce the mag- netic properties of the parts close to the magnet

��1 -Magnet

���Copper spokes

��Candle N 6!ock

��the wheel that revolves is made of a piece of heavy iron wire, which is held together with copper spokes fitted in a cork A. Through the center of this cork a large pin is placed,, about which the wheel rotates. The lower end of the pin is stuck into another cork B, which is glued to the base. A strong horseshoe magnet is then sup- ported on a block of wood near the rim of the wheel as shown. A small alcohol lamp is then placed under the rim of the wheel, care being taken that it is not placed too near the magnet poles, as it would heat them and destroy a large part of the magnetism contained in them.

As soon as the portion of the wheel directly over the lamp becomes heated, the wheel will begin to turn, the heated portion revolving away from the magnet. This is because the heated portion has lost some of its ability to be attracted by the magnet, therefore it moves or is pushed away by the cool metal. — Alexander V. Bollerer.

��An

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��Undercoating for Copper Hold Paint

COPPER does not hold paint well, hence it must be treated with some substance that will take the paint, or left to weather a year or more. A good primer is boiled linseed oil, to which add a little Japan gold size. Apply one coat and let it stand about one week, then apply the paint over it.

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