58{) 



Popular Science Monthli/ 



New Method of Mounting Un- 

 breakable Watch Crystals 



TO overcome the inevitable loosening 

 of the crystal in watches suitable for 

 soldiers' wear one manufacturer clinches 

 the rim into the crystal as shown in the 

 accompanying illustration. The crystal 

 employed is likewise 

 made of a compound 

 that will not burn, 

 thus forming an ideal 

 device for wear in 

 the open or where 

 the watch is liable to 

 receive hard knocks. 



I 



This crystal is clamped into the 

 watch rim to prevent loosening 



Acetylene Trench Gun — It's a 

 Great Thrower of Shells 



ACETYLENE gas does not work well 

 . as an engine fuel. It is too ex- 

 plosive. However, a Paris inventor, R. 

 A. Brevaire, would turn this to good use 

 in a trench-gun. 



The lower part of his 

 machine consists of a 

 chamber into which air is 

 forced under pressure, or 

 sucked in by the rush of 

 an outgoing shell. Hav- 

 ing thus filled the cham- 

 ber with air, the operator 

 next admits a small 

 quantity of acetylene gas 

 by means of a valve. Air 

 and the gas intermingle 

 forming a highly explo- 

 sive mixture. This is set 

 off at will by means of a 

 spark plug and a suitable 

 coil. Shells are inserted 

 in the gun by dropping 

 them through the muzzle, 

 rear-end foremost. If the 

 gun-barrel is unrifled, 

 wings at the base of the 

 shell make it spin and fly 

 true. A sound-deadening 

 chamber is fastened to the 

 outer end of the gun; it is 

 built on the principle of an 

 automobile muffler. 



This gun is new in being 

 the first trench gun to use 

 gas as an explosive. 



Poisonous and Harmless Mush- 

 rooms Difficult to Distinguish 



N a special bulletin published by the 

 U. S. Department of Agriculture 

 special emohasis is laid upon the fact that 

 there is no simple test for distinguishing 

 between edicle and poisonous mushrooms. 

 Many of the alleged 

 distinguishing marks 

 used by farmers, 

 dealers and purchas- 

 ers of mushrooms to 

 differentiate between 

 edible and poisonous 

 mushrooms are con- 

 sidered by the ex- 

 perts of the Depart- 

 ment entirely fallacious or too unreliable 

 to be used with safety. The only safe 

 mushrooms to eat are those gathered by a 

 collector who knows exactly what he is 

 doing. Only such mushrooms should 

 are known to be non- 

 all mushrooms, which in 

 any way differ from the 

 known type of edible va- 

 rieties should be left 

 severely alone. Every 

 season there are numerous 

 fatalities from eating the 

 poisonous varieties. 



Diagram and illustration 

 of a new acetylene trench 

 mortar, fitted with silen- 

 cer and recoil mechanism. 

 Acetylene is too explosive 

 for automobiles, but this 

 is a virtue in guns 



be picked as 

 poisonous and 



Silencer 



