256 



ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1913. 



from it. The second fork is, in fact, a structure particularly well 

 adapted to gather up the energy of the sound waves which reach it, 

 receiving from each wave a small portion of energy and accumulating 

 such energy until the fork itself is brought into palpable vibration. 

 By applying this principle in wireless telegraphy — that is, by causing 

 the rate of vibration or frequency of the electrical waves to be the 

 same in the transmission and in the receiving antennae systems, con- 

 structing both to possess a normal rate as if they were to be electrical 

 tuning forks of the same pitch — the amplitude of the received im- 

 pulses is so greatly increased that signal strength is reached where 

 otherwise failure would have resulted. The one thing which has 

 characterized the more recent advances in wireless telegraphy has 

 been the accuracy of tuning and the removal of disturbing influences 

 which would interfere with the tuning. 



Formerly the transmitting circuit was excited by means which 

 tended to disturb the actual normal rate. If excited inductively, the 



inducing or primary 

 F"i6. 22. circuit had a rate of 



its own, which was 

 apt to interfere with 

 that of the vibrating 

 antenna system. 

 However, what is 

 known as loose coup- 

 ling (fig. 20), in- 

 stead of close coup- 

 ling (fig. 19), to the 

 primary or exciting 

 circuit causes such 

 confusion of rates to be nearly negligible if, particularly in the 

 exciting circuit, the current is well damped, as it is termed, or con- 

 fined to a single brief impulse as far as possible. In such case the 

 antenna circuit, in transmitting, acts as if it were a bell struck with 

 a sudden quick blow, and it vibrates at its own rate without dis- 

 turbance or interference. At the receiving end (and there maj^ be. 

 of course, many receivers in the space around the transmitting 

 antenna), the "listening-in" process consists in adjusting the rate of 

 vibration of the receiving circuit by variable condensers or induc- 

 tances, so that the maximum loudness of the received signals is at- 

 tained. The tw^o systems, transmitting and receiving, are then in tune. 

 Accuracy of tuning is evidently very important if stations are to 

 be simultaneously transmitting when near together, as only in that 

 way can one station send out energy without interfering with the 

 other; the particular receiver for w^hich the signals are intended be- 

 ing tuned for the particular antenna sending these signals. In spite 



