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. 



