796 



Popular Science MuJttJily 



under the village had an area of some 

 50 square meters (about 500 sfj. ft.). It 

 was a task which took the French over 

 two months to accomplish, for there were 

 immense difficulties encountered in 

 the way of avoiding enemy mining 

 parties and transporting material 

 necessary for making the work secure. 

 As the work progressed, electric wiring 

 was installed for illuminating the 

 dark recesses of the excavation. Final- 

 ly the large cavern of the mine under 

 the village of Dompierre was stored 

 full of explosives — enough, in 

 fact, to blow the entire village 

 to atoms. Electric fuses were 

 installed, from which under- 

 ground wires led back to 

 General Headquarters. Thus 

 the general of the division, by 

 pressing a small electric but- 

 ton ten kilometers distant, 

 blew up the German village of 

 Dompierre. He heard the 

 five seconds later and knew 

 first stroke of the great Picardy offensive 

 had been a success. 



A^ 



The paint brush 

 suspended within 

 the oil-can holder 



explosion 

 that the 



To Prevent Asphaltum in Cans 



from Evaporating 

 SPH.'XLTLIM is used extensively 

 about electrical apparatus and where 

 anyone has to do with the making 

 up of coils, and the like, a can of this 

 material will be found at hand. The 

 brush and liquid will likewise be 

 found in a condition that renders 

 them unusable until thinned with 

 drier. Just an ordinary oil-can 

 makes a convenient holder for the 

 liquid and brush. The handle of the 

 brush is inserted in the spout, 

 as shown, where it keeps the 

 brush part in the liquid. Air 

 cannot enter, hence there is 

 no evaporation. This holder 

 is especially useful for the 

 home work-shop where the 

 asphaltum is used only occa- 

 sionally and is kept in small 

 tiuantities. The brush is kept 

 n a workable condition. 



soft and 



Making an Inductance Switch for 

 Radio Work 



r 



I lap mat 

 niters the air 



A Simple Plan to Avoid Clouded and 

 Grimy Ceilings 



" i\' many resi- 

 dences and pub- 

 lic buildings where 

 hot water or steam 

 radiators are used, 

 the wall abo\e and 

 behind the radia- 

 tors and also the 

 ceiling al)ove them 

 e\entually become 

 clouded and grinn-. 

 Why? Because the air of the rooms is 

 drawn to these warmest points, rising 

 between the coils and going directly 

 ujiward before spreading out to circulate 

 through the rest of the room. As they 

 strike the wall and ceiling the colunms of 

 warm air deposit their dust. 



A remedy was found by one house- 

 keeper who made simple mats or covers 

 of coarsely woven l)urla|) in colors to 

 harmonize with the furnishings. Placed 

 on the radiator these opcn-wea\e hem- 

 med ilollis allow the air to rise through 

 them, but sift or filter out the dust, which 

 is remov<'d by an occasional washing. 



w 



WES using switches it often hap- 

 pens that trouble is found in 

 making coiuiection to the lever. Solder- 

 ing is about the best method, but it is 

 often inconvenient. By using the device 

 shown in the sketcit this trouble will be 

 avoided. 



In the drawings, A is the regular 

 brass arm of the switch; the arm B is 



Small switch made of brass strips to form 

 connections to the lever contact points 



fastened dircctK' under the arm A and 

 re\'oKes with it, so that when A is on a 

 switch point li is making contact with 

 the brass strip C. 



The piece C may be cut from sheet 

 brass or copper. It is held to the 

 board by the posts D from which the 

 comiection is taken. 



