Page:Popular Science Monthly Volume 88.djvu/807

 Popular Science MontJily

��779

��such a way as to get their true effective values. The relation expressed by this rule is used often to determine the resistance when the damping, inductance and capacity are known; to do this, the damping must be measured in some other way. The method most utilized depends upon the fact that feebly damped circuits give much sharper tuning than those which are highly damped. In a later article this will be explained more fully, and various ex- amples of tuning measurements will be given; for the present it will be sufficient to point out that the sharpness of tuning depends upon the amount of energy that may be accumulated in an oscillat- ing circuit by resonance. Every wave of a wave-train adds its share to the energy being stored, hence it becomes almost obvious that the more waves there are in a train, the more energy will be stored. It is apparent from the pendulum experiments that the feebler the damping of an oscillating system, the more oscillations it will complete before it comes to rest. Since the waves in a wave- train correspond to the number of complete current oscilla- tions in the antenna as a result of the spark generating that wave-train, it is seen that the less damped the antenna current, the more waves per train. Thus the less the damping, the sharper the tuning.

Fig. 5 is a curve which shows the number of complete oscillations in a wave-train of any normal decrement before the amplitude is reduced to ten per cent of its original value. By looking up the decrement along the horizontal line, then tracing upward until the curve is intersected directly over the assumed decrement value, and then following the horizontal line to the scale at the left, the various desired values may be found. Thus, for decrement 0.2 there are only 12 complete oscilla- tions before the amplitude has fallen off nine-tenths, while for decrement 0.02 there are about 112 oscillations. As the decrement grows smaller the number of oscillations rises rapidly; for zero decre- ment the number would be infinite — the oscillations would be completely sustained and would not die away until the circuit was opened.

��A National Wireless Association

THE National Amateur Wireless Association, headed by Guglielmo Marconi, inventor of wireless telegraphy, has entered the field of radio communica- tion for the expressed purpose of promot- ing group, or co-operative, working among amateurs. The organization is a comprehensive one, aiming to direct and standardize radio experiment through- out the United States by arranging with each member for progressive courses of study and later through grouping the most promising radio enthusiasts with active co-workers and guiding the experi- ments along productive lines. The de- velopment of radio engineers from sincere investigators who are hampered by facilities for higher training is to be promoted by a series of specially de- signed experiments, supplemented by a monthly bulletin service.

Military wireless signaling is a branch of instruction to be given a prominent place in the program. Arrangements have been made for amateur clubs throughout the country to affiliate with military organizations as accredited members and officers of signal corps. This branch of training is under the direction of Major William H. Elliott, Adjutant-General of the Junior Ameri- can Guard and one of the vice presidents of the Association. Several signal corps batallions have already been formed and are training to serve in the proposed third line of defense for the nation. Summer camps have been secured and field maneuvers will be featured in the vacation months.

From the New York headquarters of the Association, announcement is made that every amateur who is properly endorsed may secure membership as an individual. According to abilities and geographical location, members are en- tered for eligibility in some existing local club, state or inter-state association, and when these have secured recognition, a representative is appointed to the Na- tional Council with a voice in the management of the governing body.

In the unusual growth in popularity of wireless lies a possible source of bene- fit to the nation. Every skilled amateur could render great service to his country in time of war.

�� �