Page:Popular Science Monthly Volume 91.djvu/327

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Popular Science Monthly

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��A Drip- Pan Alarm for the Ice-Box Drain

THE illustration shows a very neat and easily constructed drip-pan alarm which can be made by the home worker at a very slight expense. A small piece of glass tubing is run up through a cork float, on top of which is secured a light round copper washer. The cork with its guide hangs down into the pan from the under side of the base-piece of the re- frigerator as shown in the illustration.

��An Amplifying Electrostatic Radio Receiver

��IN THE development of radio telegraphy inventors have constantly striven to produce detectors or receivers which would be not only sensitive, but also rugged and easy to adjust and to keep in adjustment. Some of the instruments in common use meet these requirements, but in general the more sensitive of them are rather deli- cate in operation and seem likely to be rendered inoperative, or at least less

���The cork float details and the manner of hanging it to the underside of a refrigerator to sound a bell when the drip -pan is about full and there is danger of it overflowing

��It will be noticed at A that the perma- nent contact points or wires are so high that they in no way interfere with the sides of the pan when it is withdrawn to be emptied. The batteries of the door-bell circuit are utilized to operate the buzzer or bell of the pan-alarm, as at B. A simple one-point switch is placed in the circuit for con- venience if the pan cannot be emptied at once, the contacts being so arranged that the alarm will sound continuously after the water is within I in. of the top of the pan. — F. W. Bentley.

��Treating Cardboard Tubes for Tuners on Wireless Apparatus

A GOOD way to make a cardboard tube non-shrinkable is to give it several coats of varnish before commencing the winding. — Charles Wildinger.

��sensitive, by receipt of loud signals or heavy strays. It has often been said that a wide departure from present principles would be necessary before an ideal receiver could be produced.

A device shown in 1916, United States patent to R. A. Fessenden, number 1,179,906, is interesting in this connection. A diagrammatic view of this instrument shows that the apparatus consists essen- tially of a combined electrostatic telephone and amplifying carbon microphone. The antenna 1 is connected through the tuned transformer primary 2 to earth 3, and coupled to the primary is the secondary coil 4. A secondary loading coil 5 is in series with this last-named inductance, and both are shunted by the static receiver con- sisting of the thin movable diaphragm or plate 6 placed close to, but not touching, the fixed plate 7.

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