Page:Popular Science Monthly Volume 88.djvu/975

 Popular Science Monthly

��947

��The Construction of an Automatic Battery Circuit-Breaker

AN automatic circuit-breaker and its L operation are depicted in the ac- companying diagrams.

Referring to Fig. I,^ is a wooden base 4 ins. by 2 ins. by j^ in., 5 is a brass strip }/s in. by }i in., bent as shown so as to stand 2^i ins. above the base. The magnet M is 2)4 ins. by ^ in. and wound with 4 layers of No. 16 annuncia- tor wire and screwed to 5 at a point 23^ ins. above the base. The strips C and D are of spring brass, 1/64 in. thick by ^^ in. wide, their ends being bent as shown in Fig. II. The strip D, has a piece of soft iron E screwed fast to it at a point opposite the magnet core. The strip C is bent so as to have a tendency to spring up when D is drawn into the magnet. The wiring is clearly shown in Fig. I,

In operation, the circuit-breaker is placed in series with the battery and the circuit which is to be protected, close to the battery. Should a short- circuit occur on the line, the excess current flowing through the magnet energizes it more strongly than when the normal current flows, drawing D in- ward, thus releasing C, and so breaking the circuit. — E. B. Wilson.

����When the postman raises the mail-box Ud a bell rings in the house

��When a short-circuit occurs, the circuit

is broken automatically by means of this

simple device

How to Make a Rural Mail-Box Alarm

TO those living in rural or suburban districts, where the mail is deposited in a wooden mail-box by the roadside, the device here described will be of interest. The idea is to have an announcing bell at the house when the mail is placed in the box, and thus make a long wait in the cold unnecessary. An electric bell is put in circuit as depicted, using a dry battery as a source of energ>\ It is advisable to use a roll of insulated bell tape to insulate the wires properly. Two dry cells will be sufficient for any distance up to 200 ft. Cut a thin brass strip and bend at the center. Fasten to the top-extension of the mail-box and connect with the battery. Replace the wooden cover of the mail-box by a brass or metal one. Both the brass strip and metal cover must, of course, be connected with the house by two separate wires. The wires to the house are simply tacked by staples on to small posts. Following is the modus operandi: As soon as the mailman lifts the lid to place the mail in the box, the metal lid comes in connection with the brass strip and closes the circuit, operating the announcing bell at the house. — Wm. Warnecke, Jr.

Japanese Wireless Telephone

THE Japanese Navy is equipped with apparatus for radio telephones, with which wireless speech can be transmitted dependably about- ten miles and often three times this distance.

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