The whole is connected up and mounted on a baseboard as per sketch, the contact posts being of 1/4 in. by 1/2 in. brass, bent into shape and provided with platinum tipped thumb screws.  The advantage of this style of an interrupter is that at each stroke there is a wiping effect at the heavy current contact which automatically cleans off any carbon deposit.

In the wiring diagram, A is the circuit breaker; B, the induction coil, and C, the battery.  —­Contributed by A. G. Ward, Wilkinsburg, Pa.

** Spit Turned by Water Power [102]

Many of the Bulgarian peasants do their cooking in the open air over bonfires.  The illustration shows a laborsaving machine in use which enables the cook to go away and leave meat roasting for an hour at a time.  The

[Illustration:  For a Summer Camp]

illustration shows how the spit to which the meat is fastened is constantly turned by means of a slowly moving water wheel.  Some of our readers may wish to try the scheme when camping out.  The success depends upon a slow current, for a fast-turning wheel will burn the meat.

** A Short-Distance Wireless Telegraph [102]

The accompanying diagrams show a wireless-telegraph system that I have used successfully for signaling a distance of 3,000 ft.  The transmitter consists of an induction coil, about the size used for automobiles, a key or push-button for completing the circuit, and five dry batteries.  The small single-point switch is left open as shown when sending a message, but when receiving it should be closed in order that the electric waves from the antenna may pass through the coherer.  The coherer in this case is simply two electric-light carbons sharpened to a wedge at one end with a needle

[Illustration:  Wiring Diagram for Wireless Telegraph]

connecting the two, as shown.  An ordinary telephone receiver is connected in series with the coherer, as shown.  To receive messages hold the receiver to the ear and close the switch, and answer by opening the switch and operating the key. —­Contributed by Coulson Glick, Indianapolis.

** Automatic Draft-Opener [102]

A simple apparatus that will open the draft of the furnace at any hour desired is illustrated.  The parts are:  A, furnace; B, draft; C, draft chain; D, pulleys; E, wooden supports; F, vertical lever; G, horizontal lever; H, cord; I, alarm clock; J, weight.  K shows where and how the draft is regulated during the day, the automatic

[Illustration:  Draft Regulator]

device being used to open it early in the morning.  The spool on the alarm clock is fastened to the alarm key by sawing a slit across the top of the spool and gluing it on.  When the alarm goes off a cord is wound up on the spool and pulls the horizontal lever up, which releases the vertical lever and allows the weight to pull the draft open.  —­Contributed by Gordon Davis, Kalamazoo, Mich.