** Combined Door Bell and Electric Alarm [114]

This device consists of a battery and bell connection to an alarm clock which also acts as a door bell, the whole being mounted on a board 18 in. long and 12 in. wide.  Referring to the sketch accompanying this article, the letters indicate as follows:  A, bell; B, battery ; C, switch; D, V-shaped copper strip; E, copper lever with 1-in. flange turned on one side, whole length, 4 in.; F, spring to throw lever E down in V-shaped piece to make connection; G, lever to hold out E when device is used as a door bell; lines H, go, one from bell, A, and one from battery, B, to the door; I, shelf for clock.

See that the ring in the alarm key of the clock works easily, so that when it is square across the clock it will drop down.  Fasten a piece of copper about

[Illustration:  Wiring Disgram]

1 in. long to key, then wind the alarm just enough so that the key stands straight up and down.  Place the clock on the shelf and the key under the flange of lever E. Pull lever G down out of the way and close the lever on the switch.  The alarm key will turn and drop down, letting lever E drop into the V-shaped piece D and make connection.

For the door-bell connection close lever on switch C, and put G up so that D and E do not come in contact.  If anyone is ill and you do not want the bell to ring, open switch C.

The wiring for this device may all be on the back of the board.  The switch and levers are fastened with small screw bolts, which allows wiring at the back.  Saw two spools in half and fasten the halves to the four corners of the board at the back, and the apparatus may be put up where one likes.

**v To Build a Small Brass Furnace [115]

Bend a piece of stout sheet iron 23 in. by 12 in. round so that the inside

[Illustration:  Furnace]

diameter is 7 in., and then rivet the seam.  Fit in a round piece of sheet iron for the bottom.  Make a hole about the size of a shilling in the side, 2 in. from the bottom.  This is for blowing.

Line the furnace, bottom and sides with fire-clay to a depth of 1/2 in.  Use charcoal to burn and an ordinary bellows for blowing, says the Model Engineer, London.  The best blast is obtained by holding the nozzle of the bellows about an inch from the hole, instead of close to it.

** Avoid Paper Lamp Shades [115]

Don’t wrap paper around a lamp for a shade.  You might go away and forget it and a fire might be started from the heat.  Use a glass or metal shade.  That is what they are for.

** Why Gravity Batteries Fail to Work [115]

Many amateur electricians and some professionals have had considerable trouble with gravity batteries.  They

[Illustration:  Setting Up a Gravity Battery]