[Illustration:  Electric Fire Alarm]

At the house an electric bell is placed wherever convenient.  Several battery cells, of course, are also needed.  Dry batteries are most convenient.  The battery cells and bell are connected in the usual manner, and one wire from the bell and one from the battery are strung to the barn and connected to the binding posts D D.

If a fire occurs in the hay-mow the blaze will generally shoot toward the gable soon after it starts, and will then burn the string C, which allows the weight B to fall and pull the brass spring against the iron piece E, which closes the circuit and rings the bell in the house.

If desired, the string may be stretched back and forth under the roof several times or drawn through any place that is in danger of fire.  —­Contributed by Geo. B. Wrenn, Ashland, Ohio.

** How to Make a Small Electric Furnace [48]

Take a block of wood and shape into a core.  One like a loaf of bread, and about that size, serves admirably.  Wrap a layer of asbestos around it and cover this with a thin layer of plaster-of-paris.  When the plaster is nearly dry wind a coil of No. 36 wire around it, taking care that the wire does not touch itself anywhere.  Put another course of plaster-of-paris on this, and again wind the wire around it.  Continue the process of alternate layers of plaster and wire until 500 ft. or more of the latter has been used, leaving about 10 in. at each end for terminals.  Then set the whole core away to dry.

For a base use a pine board 10 in. by 12 in. by 1 in.  Bore four holes at one end for binding-posts, as indicated by E E. Connect the holes in pairs by ordinary house fuse wire.  At one side secure two receptacles, B B, and one single post switch, C. Place another switch at I and another binding-post at F. The oven is now ready to be connected.

Withdraw the wooden core from the coils of wire and secure the latter by bands of tin to the board.  Connect the ends of the wire to binding-posts E and F, as shown.  From the other set of binding-posts, E, run a No. 12 or No. 14 wire, connecting lamp receptacles, B B, and switch, C, in parallel.  Connect these three to switch, D, in series with binding-post, F, the terminal of the coil.  Place 16-cp. lights in the receptacles and connect the fuses with a 110-volt lighting circuit.  The apparatus is now ready for operation.  Turn on switch, D, and the lamps, while C is open.  The coil will commence to become warm, soon drying out the plaster-of-paris.  To obtain more heat

[Illustration:  Electric Furnace]

open one lamp, and to obtain still more open the other and close switch C.  —­Contributed by Eugene Tuttles, Jr., Newark, Ohio.

** How to Make an Ammeter [49]

Every amateur mechanic who performs electrical experiments will find use for an ammeter, and for the benefit of those who wish to construct such an instrument the following description is given:  The operative principle