62 



POPULAR SCIENCE MONTHLY 



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every part of sucli a wire when a spark jumps between the ter- 

 minals S of the coiL All that is necessary to do is to pass the wire 

 through a sensitive film and to develop the film. The accompany- 

 ing photograph (Fig. 3) was taken at the top of such a wire, by 

 means of a very powerful apparatus at my command. When the 

 photograph is examined with a microscope the arborescent 

 electric lines radiating from the wire, like the rays of light 

 from a star, exhibit a beautiful fernlike structure. These 

 lines, however, are not chiefly instrumental in transmitting 

 the electric pulse across space. 



There are other lines, called magnetic lines of force, 

 wdiich emanate from every ])ortion of the vertical w'ire W 

 just as ripples spread out on the surface of placid water when 

 it is disturl:)ed by the fall of a stone. These magnetic rip- 

 ples travel in the ether of space, and when 

 they embrace a neighboring wire or coil 

 produce similar ripples, which whirl 

 about the distant wire and produce 

 in some strange way an electrical 

 current in the wire. These mag- 

 netic pulsations can travel great 

 distances. 



In the photographs of these 

 magnetic Avhirls, Fig. 4 is the 

 whirl produced in the circuit C by 

 the battery B (Fig. 2), while Fig. 

 5 is that produced by electrical 

 sympathy, or as it is called induc- 

 tion, in a neighboring wire. These 

 photographs were obtained by pass- 

 ing the circuits through the sensi- 

 tive films, perpendicularly to the 

 latter, and then sprinkling very 

 fine iron filings on these surfaces 

 and exposing them to the light. 

 In order to obtain these photo- 

 graphs a very powerful electrical 

 current excited the coil C (Fig. 2), and the neighboring circuit W 

 (Fig. 5) was placed very near the circuit W. 



When the receiving wire is at the distance of several miles 

 from the sending wire it is impossible to detect by the above 

 method the magnetic ripples or whirls. We can, however, detect 

 the electrical currents which these magnetic lines of force cause 

 in the receiving wire; and this leads me to speak of the discovery 



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i;. -In represeiUB :i in;)je coinpictu elec- 

 trical arrangement of the receiver cir- 

 cuit. The vertical wire, W, is con- 

 nected to one wire of the coherer, L. 

 The other wire of the coherer is led to 

 the ground, G. The wires in the co- 

 herer, L, are separated by fine metallic 

 jiarticles. B represents a battery. Yl, 

 an eiectro-magnet which attracts a 

 piece of iron, A (armature), and closes 

 a local battery, B, causing a click of 

 the sounder (electro-magnet), S. The 

 magnetic waves (Fig. 5) embracing 

 the wire, W, cause a pulsation in this 

 wire which produces an electrical dis- 

 turbance in the coherer analogous to 

 tiiat shown in Fig. 3, by means of 

 which an electrical cuiTent is enabled 

 to pass through the electro-magnet, K. 



