Page:Popular Science Monthly Volume 90.djvu/806

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790

��Popular Science Monthly

��accompanying diagram will illustrate how this may be done. The large lamps are ordinary iio-volt bulbs, while the small one is a battery lamp of 6 to lo volts.

This experiment well illustrates the idea of difference of potential. When the tip of the wire is exactly in the center of the jar, the circuit is "balanced" and no current flows in the circuit of the small lamp. This differential method of control has one marked advantage over the rheostat in experimental work in that it is possible to start with absolute zero. — ^John D. Adams.

��A Homemade Floor Push Button for Annunciators

A SIMPLE method of making an ordi- nary push button serve as a floor button for summoning the maid from the kitchen to the dining-room is shown in the il- lustration. Such a push has been in use for several years and is still in commission. The button was connected with the door bell sys- tem in such a manner that all the wiring neces- sary was across the small space from the button in the floor to the regular line.

The button A was placed in a small bracket nailed to the adjoining joist D and a hole bored through the floor C. A short stick — a lead pencil will do — was passed through the hole and allowed to "rest on the button, as at B. The wires E lead to the bell circuit. A prearranged signal dif- ferentiates between a call from the front door and one from the dining-room or kitchen. — Philip Myers.

���Push button on joist with floor connection

��Imitating Hard Rubber with Fiber as a Base

THERE are numbers of wireless ama- teurs and electrical experimenters who are desirous of using hard rubber panels and bases, but who are unable to pay the almost prohibitive prices. Ordinarily, fiber cannot be substituted, for it has a tendency to warp and is very dull in finish. If, how-

��ever, the instructions as given are care- fully followed out the resulting piece of fiber will be so nearly like hard rubber that it will take a close examination to detect the difference.

The first operation is in smoothing down the rough surface with a piece of No. i sandpaper. When it feels smooth to the touch, continue with No. oo emery paper until it shines in spots, then wipe with a cloth and finish with a cleaning compound, such as is used in kitchens, smoothing lengthwise only in long strokes. Continue this until it shines all over. For the second operation wipe all the dust off with a clean cloth, and then with another cloth apply a coating of hard wax, such as is used on furniture and floors. The wax should be slightly colored with an aniline black. Allow the wax to harden for about 30 minutes and then polish with a brush, finishing with a soft flannel cloth. Apply two coats as described, not less than 6 hours apart. A perfect finish will be the result. As the wax is waterproof and not affected by any ordinary temperature, the fiber will not warp. This has been used with perfect success on a panel 25 in. long and 15 in. wide in a somewhat pretentious mahogany cabinet. — R. G. Young.

��Using a Well for a Wireless Ground Connection

WHEN a well is used for a wireless ground connection, the ground wire should be fastened to the top of an iron pipe leading to the bottom of the well by solder or by using a ground clamp. The pipe should be carefully scraped before the clamp is put in place. If it is desired to make connection directly with the water, brass and copper wire must be avoided because they have a bad effect upon the water. Often a well-ground of this sort will improve the range of an isolated station. — Otto Klatt.

Holding the Telephones Tightly Against the Ears

A COIL of wire or a brass spring slipped on the cord to the wireless telephones will hold them firmly against the ears. When in use the spring or coil is slipped up over the leads and brought up under the chin. This not only holds the telephones in place, but also eliminates trouble from noise of wind, passing wagons and the like. — G. P. KoMP, Jr.

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