454 



Popular Science Monthly 



A 



Finding: the Positive Wire 



N easy and 

 simple way 

 to find out which 

 wire from a 

 storage battery 

 is positive and 

 which is nega- 

 tive is the fol- 

 lowing : 



Take a glass 

 tumbler and draw some of the electro- 

 lyte from the battery, filling the tumbler 

 about half full. Take two strips of 

 clean lead and attach them to the two 

 wires. Drop the leads into the solution, 

 suspending them free in it, and switch 

 on the current. After two or three min- 

 utes turn off the current and examine 

 the .pieces of lead. The one attached to 

 the positive wire will be covered with a 

 fine brownish deposit, while the nega- 

 tive end will be clean. The illustration 

 herewith shows the arrangement. 



How to Prolong the Life of 

 Battery Cells 



BATTERIES used for gas engine 

 ignition are usually connected in 

 series parallel, or, in opposition. This 

 is the best method of connecting them, 

 since a larger current can be obtained. 

 One disadvantage in this method of 

 connecting cells is that, if the cells are 

 left in opposition when not in use, they 

 very quickly "die." The accompany- 

 ing diagram shows a handy method of 

 connecting cells so they will be in par- 

 allel only when 



To Spark Coil 



the switch is 

 closed. When the 

 switch is opened 

 the parallel con- 

 nection, as well as 

 the external cir- 

 cuit, will be broken. The arrows indi- 

 cate the direction of the current when 

 the switch is closed. 



The Obligation to Secrecy. 



ALTHOUGH the United States 

 Government does not require ex- 

 perimental radio receiving stations or 

 their operators to hold Federal li- 

 censes, the law as to secrecy of re- 

 ceived messages is enforced upon 

 them. This law states in effect that 



no persons shall divulge or publish the 

 contents of any radio messages re- 

 ceived or known by them, and provides 

 a fine of $250 and three months im- 

 prisonment for violations. 



Springless Electric Bell 



AN electric bell can be made which 

 will operate without springs, by in- 

 stalling the armature between two op- 

 posed sets of magnets. The resistance 

 of opposing sets of magnet coils should 

 be equal, about 150 ohms when the bell 

 is operated on low voltage, and 200 ohms 

 when a higher voltage is used. The dia- 

 gram of necessary connections is shown 

 in the accompanying illustration. 



The action of the magnets makes the use of 

 springs unnecessary 



Photographic Records Still 

 Impracticable 



HIGH speed automatic wireless tele- 

 graphy in which a photographic re- 

 corder is used for the receipt of messages 

 has often been attempted. Under favor- 

 able conditions signals of a moderate 

 strength can be recorded at 80 or 100 

 words per minute, but presence of the 

 slightest "static" makes great trouble. 

 Even normal static, as it is heard during 

 the summer in Northern latitudes, is suf- 

 ficiently troublesome to make practical 

 working impossibile. Other methods, 

 such as those using phonographs or tele- 

 graphones, for recording the incoming 

 signals, have proved successful over mod- 

 erate distances. The large number of 

 messages which can be sent in a short 

 time by automatic working makes the 

 problem attractive to radio companies. 



