254 SIGNALING THROUGH SPACE WITHOUT WIRES. 



the Morse key K. "Row, whenever the key K is depressed sparks pass 

 between 1, 2, and 3, and since the system A B contains capacity and 

 electric inertia, oscillations are set up in it of extreme rapidity. The 

 line of propagation is D d, and the frequency of oscillatio/i is probably 

 about 250 millions per second. 



The distance at which effects are produced with such rapid oscilla- 

 tions depends chiefly on the energy in the discharge that passes. A 

 6-inch spark coil has sufficed through 1, 2, 3, up to 4 miles, but for 

 greater distances we have used a more powerful coil — one emitting 

 sparks 20 inches long. It may also be pointed out that this distance 

 increases with the diameter of the spheres A and B, and it is nearly 

 doubled by making the spheres solid instead of hollow. 



The receiver. — Marconi's relay (fig. 2) consists of a small glass tube 

 4 centimeters long, into which two silver pole pieces are tightly fitted, 

 separated from each other by about half a millimeter — a thin space 

 which is filled up by a mixture of fine nickel and silver filings, mixed 

 with a trace of mercury. The tube is exhausted to a vacuum of 4 milli- 

 meters, and sealed. It forms part of a circuit containing a local cell 

 and a sensitive telegraph relay. In its normal condition the metallic 

 powder is virtually an insulator. The particles lie higgledy-piggledy, 

 anyhow, in disorder. They lightly touch each other in an irregular 

 method, but when electric waves fall upon them they are "polarised," 

 order is installed. They are marshaled in serried ranks, they are sub- 

 ject to pressure — in fact, as Prof. Oliver Lodge expresses it, they 

 "cohere" — electrical contact ensues and a current passes. The resist- 

 ance of such a space falls from infinity to about 5 ohms. The electric 

 resistance of Marconi's relay — that is, the resistance of the thin disc of 

 loose powder — is practically infinite when it is in its normal or dis- 

 ordered condition. It is then, in fact, an insulator. This resistance 

 drops sometimes to 5 ohms, when the absorption of the electric waves 

 by it is intense. It therefore becomes a conductor. It may be, as 

 suggested by Professor Lodge, that we have in the measurement of the 

 variable resistance of this instrument a means of determining the inten- 

 sity of the energy falling upon it. This variation is being investigated 

 both as regards the magnitude of the energy and the frequency of the 

 incident waves. Now such electrical effects are well known. In 1866 

 Mr. S. A. Varley introduced a lightning protector constructed like the 

 above tube, but made of boxwood and containing powdered carbon. It 

 was fixed as a shunt to the instrument to be protected. It acted well, 

 but it was subject to this coherence, which rendered the cure more 

 troublesome than the disease, and its use had to be abandoned. The 

 same action is very common in granulated carbon microphones like 

 Hunning's, and shaking has to be resorted to to decohere the carbon 

 particles to their normal state. M. E. Branly (1890) showed the effect 

 with copper, aluminum, and iron filings. Prof. Oliver Lodge, who 

 has done more than anyone else in England to illustrate and pop- 



