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POPULAR SCIENCE MONTHLY. 



across the space which separates the coils. Doubtless if man knew 

 all the capabilities of this simple apparatus he might talk to China, 

 or receive messages from the antipodes. He now, bj means of it, 

 analyzes the light of distant suns, and produces the singular X 



Flo. 1. — Disposition nf batteries and coils at the sending station, showing the arrangement of 

 the vertical wire and the spark gap. 



rays w^hich enable him to see through the human body. By means 

 of it he already communicates his thoughts between stations thou- 

 sands of miles apart, and by means of its manifestations I hope to 

 make this article on W'ireless telegraphy intelligible. My essay can 

 be considered a panegyric of this buried form-^a history of its 

 new life and of its unbounded possibilities. 



For convenience, one of the coils of the transformer is placed 

 inside the other, and the combination is called a Ruhnikorf coil. 

 It is represented in the accompanying photograph (Fig. 1), with 

 batteries attached to the inner coil, while the outer coil is con- 

 nected to two balls, between which an electric spark jumps when- 

 ever the battery circuit is broken. In fact, any disturbance in the 

 battery circuit — a weakening, a strengthening, or a break — pro- 

 vided that the changes are sudden, produces a corresponding 

 change in the neighboring circuit. One coil thus responds to the 

 other, in some mysterious way, across the interval of air which 

 separates them. Usually the coils are placed very near to each 

 other — in fact, one embraces the other, as shown in the photo- 

 graph. 



The coils, however, if placed several miles apart, will still re- 



