WIRELESS TEANSMISSION OF ENERGY— THOMSON. 255 



may not be curved. In the curved surface of the ocean the zones of 

 charge continually expanding, plus and minus, respectively, are still 

 connected by the electrostatic lines above them, and the moving 

 charges still generate the same magnetic field as they traverse radi- 

 ally or outwardly in the curved instead of the plane sheet (fig. 22), 

 and this curved conductor still guides the energy, just as the wire 

 does in ordinary transmission. It would seem, if this is the correct 

 view, that at a distance comparable with that of a quadrant of the 

 earth's circumference the form of the wave would be such as to cause 

 the stress lines to lean backward with respect to the surface, tending 

 to keep their original relation to the transmitting antenna as they 

 were detached therefrom (fig. 22, at L). This assumes that the 

 A'elocity of transmission is the same as that of the speed of light, 

 both for the currents in the sea and for the stresses above it. 



Marconi's success as a wireless pioneer depended largely upon the 

 choice of a sufficiently sensitive receiver. Two elements are necessary 

 in the receiver. First, a conducting structure which gathers up the 

 energy from the medium, the ether, above the earth's surface. The 

 other element is a sufficiently delicate means for detecting the slightest 

 changes of electrical condition, not only actuated by what little 

 energy is received, but so modifjdng it that it can operate a signal 

 which can be seen or heard. Usually the receiving antenna is a ver- 

 tical conducting mast or cage, like the sending antenna. In fact, 

 the functions of sending and receiving are interchangeably used on 

 the same structure; the same antenna may be at one time used for 

 transmitting and at another time for receiving. 



The receiving antenna (fig. 22) serves to relieve the electrostatic 

 stress in its vicinity, much as a lightning rod may act to relieve 

 cloud to earth stresses. If its direction could be made to follow or 

 be parallel to the actual course of the transmitted lines in the space 

 near it, it would be most effective, and if, further, it could extend 

 sidewise over a considerable extent of the wave front, it would gather 

 up more energ}\ These conditions, however, can at best be only ap- 

 proximately met. If the receiving antenna were of such a character 

 as to have no oscillation rate of its own (a damped circuit) it woidd 

 receive energ}^ in a small amount from the transmitting antenna 

 independent of the frequency, but as this would in most cases be far 

 from sufficient, it is desirable to accumulate energy in the receiver 

 from a train of waves at a definite rate. To do this the principle of 

 syntony or tuning is brought in. Everyone is familiar with the two 

 tuning forks, where one is sounded and the other is placed at a dis- 

 tance away. If the two forks are not in harmony, no effect of the 

 one fork on the other follows, but if they are accuratel}^ tuned in 

 unison, the sound of one fork at a considerable distance from the 

 other starts the second in vibration and produces an audible sound 



