Popular Science Monthly 



311 



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 the pan when it is withdrawn to be emptied.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. 



