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. 



