The tuning coil is simply a variable choking coil, made of No. 14 insulated copper wire wound on an iron core, as shown in Fig. 7.  After winding, carefully scrape the insulation from one side of the coil, in a straight line from top to bottom, the full length of the coil, uncovering just enough to allow a

[Illustration:  Aerial]

good contact for the sliding piece.  The tuning is done by sliding the contact piece, which is made of light copper wire, along the convolutions of the tuning coil until you can hear the signals.  The signals are heard in a telephone receiver, which is shown connected in shunt across the binding posts of the lamp holder with one or two cells of dry battery in circuit, Fig. 7.

[Illustration:  Details]

The aerial line, No.6 stranded, is run from binding-post B through the choking or tuning coil, and for best results should extend up 50 ft. in the air.  To work a 20-mile distance the line should be 100 or 150 ft. above the ground.  A good way is to erect a wooden pole on a house or barn and carry the aerial wire to the top and out to the end of a gaff or arm.

To the end of the aerial wire fasten a bunch of endless loops made of about No. 14 magnet wire (bare or insulated), attaching both ends to the leading or aerial wire.  The aerial wire should not come nearer than 1 ft. at any point to any metal which is grounded.

Run a wire from the other binding post, A, to the ground and be sure to make a good ground connection.

For simple experimental work on distances of 100 ft. only, an ordinary automobile spark coil can be used in place of the more elaborate coil, Figs. 1 to 4.

The above-mentioned instruments have no patents on them, and anyone is at liberty to build and use them.  The writer does not claim to be the originator, but simply illustrates the above to show that, after all, wireless is very simple when it is once understood.  The fundamental principles are that induction travels at right angles, 90 degrees, to the direction of the current.  For an illustration, if a person standing on a bridge should drop a pebble into the water below, after contact he would note circles radiating out over the surface of the water.  These circles, being at right angles, 90 degrees, to the direction of the force that caused the circles, are analogous to the flow of induction, and hence the aerial line, being vertical, transmits signals horizontally over the earth’s surface.

** Beeswax for Wood Filler [85]

When filling nail holes in yellow pine use beeswax instead of putty, as it matches the color well.

** How to Make a Lathe [86]

A small speed-lathe, suitable for turning wood or small metal articles, may be easily made at very little expense.  A lathe of this kind is shown in the cut (Fig. 1), where A is the headstock, B the bed and C the tailstock.  I run my lathe by power, using an electric motor and countershaft, but it could be run by foot power if desired.  A large cone pulley would then be required, but this may be made in the same manner as the small one, which will be described later.