Page:Popular Science Monthly Volume 88.djvu/482

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��Popular Science Monthly

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��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.

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