** Homemade Mariner’s Compass [170]

Magnetize an ordinary knitting needle, A, and push it through a cork, B, and place the cork exactly in the middle of the needle.  Thrust a pin, C, through the cork at right angles to the needle and stick two sharpened matches in the sides of the cork so that they will project downward as shown.  The whole arrangement is balanced on a thimble with balls of wax stuck on the heads of the matches.  If the needle is not horizontal, pull it through the cork to one side or the other, or change

[Illustration:  Magnetized Needle Revolving on a Pin]

the wax balls.  The whole device is placed in a glass berry dish and covered with a pane of glass.

** Brighten White Paint [170]

Add aluminum bronze to a white or light paint that is to be used for lettering on a dark ground.

** Quartz Electrodes Used in Receiving Wireless Messages [170]

[Illustration:  Details of the Receiving Instrument]

Wireless messages have been received at Washington, D.C., from Key West, Florida, a distance of 900 miles, through a receiving instrument in which two pieces of quartz of different composition were used on the electrodes.  In making an instrument of this kind the quartz can be purchased from a dealer in minerals.  One piece must contain copper pyrites and the other zincites.  The electrodes are made cupping to hold the minerals and each should have a screw adjustment to press the pieces of quartz in contact with each other.  Connect as shown in the illustration, using a high resistance receiver.  —­Contributed by Edwin L. Powell, Washington, D. C.

** How to Make a Glider [171] By Carl Bates

A gliding machine is a motorless aeroplane, or flying-machine, propelled by gravity and designed to carry a passenger through the air from a high point to a lower point some distance away.  Flying in a glider is simply coasting down hill on the air, and is the most interesting and exciting sport imaginable.  The style of glider described in this article is known as the “two-surface” or “double-decked” aeroplane, and is composed of two arched cloth surfaces placed one above the other.

In building a glider the wood material used should be straight-grained spruce, free from knots.  First prepare from spruce planks the following strips of wood.  Four long beams 3/4 in. thick, 1-1/4 in. wide and 20 ft. long; 12 crosspieces 3/4 in. thick, 3/4 in. wide and 3 ft. long; 12 uprights 1/2 in. thick, 1-1/2 in. wide and 4 ft long; 41 strips for the bent ribs 3/16 in. thick, 1/2-in. wide and 4 ft. long; 2 arm sticks 1 in. thick, 2 in. wide and 3 ft. long; the rudder sticks 3/4 in. square and 8 ft long; several strips 1/2 in. by 3/4 in. for building the vertical and horizontal rudders.  The frames for the two main surfaces should be constructed first, by bolting the crosspieces to the long beams at the places shown by the dimensions in Fig. 1.  If 20-ft. lumber cannot be procured, use 10-ft. lengths and splice them, as shown in Fig. 3.  All bolts used should be 1/8 in. in diameter and fitted with washers on both ends.  These frames formed by the crosspieces should be braced by diagonal wires as shown.  All wiring is done with No. 16 piano wire.