614 



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 



to 



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. 



