THEORY. The theoretical considerations upon which the electric wave method of wireless teleg raphy is based may be divided into two parts, namely (a) the conversion of electric oscillations into electric waves and vice versa, and (11) the propagation of electric waves throng)] space.
That portion of the transmitter which includes the aerial and Oa WWII wires and the spark-gap, 7, 8, 9 (see Fig. di, is termed the oscillator sys tem. and that portion of the receiver comprising the aerial and earthed wires and the wave de tector, 10, 11, 12, is termed the resonator syst en: When the spark passes between the balls of the spark-gap, 7, high-frequency high-potential cur rents are set up in the oscillator system; these oscillatory currents are not constant. but their amplitude dtereases from its maximum value to zero potential in geometric progression, as in dicated by the curve in Fig. 7. This is due to the damping factor in volved in the con version of the en ergy of the oscilla tions into electric waves. The fre quency of the oscil lations depends on the electrical dimen sions of the circuit: these are termed its coefficients, and consist of its electrostatic capacity, its inductance, and its resistance.
The capacity of an oscillatory system is meas ured by the quantity of electricity required to charge it to a certain critical potential where it will disrupt the air-gap, and the capacity of the system is directly proportional to the charge and inversely proportional to the potential. Induct ance is the effect of a current flowing in the oscillator system on itself, and in dealing with high frequencies this effect is very marked, so that a finite current requires time to reach its maximum value and time for the current to fall to zero. The resistance of the oscillator system finds its analogue in the frictional resistance a pipe offers to flowing water: when the cur rent is of high potential and frequency the re sistance of the system may be regarded as negligible, since the high resistance offered by the spark-gap is broken down by the spark during the period the high-frequency current is oscil lating through the system.
In the resonator system the same conditions prevail. but instead of emitting electric waves as in the case of the oscillator the electric waves impinging upon the aerial wire set up electric oscillations, and although very greatly reduced in potential compared with those originally emitted, the frequency is identical.
The mode of electric wave propagation through the ether has been deduced on two different theories. The first is based on the rectilinear propagation of electric waves. An experiment to demonstrate that electric waves traverse space in straight lines may be made by em ploying an ordinary Hertz oscillator, shown diagrammatically in Fig. 8. When high frequency currents os cillate through the sys tem spherical electric waves in the form of transverse vibrations in the ether are emitted as depicted in Fig. 0, each one being detaelled from the oscillator and propagated through space at the velocity attained by light waves, i.e. 186.500 miles per second. Where one terminal is grounded and the opposite terminal of the oscillator system is elevated, as shown in Fig. 0, the theory of rectilinear propagation as sumes that the waves are still spherical and travel in a straight line until they come in contact. with the upper stratification of rarefied air, which is a con ductor of elec tricity and there fore a non-con ductor of electric waves, in which case the waves are reflected back to the surface of the earth.
Electric waves are radiated in every direction at right angles to the oscillator system; now if a resonator system is placed in a direct visual line to the oscillator it will respond, but if the curvature of the earth intervenes as shown in the diagram Fig. 10, then the waves will be re flected from the strata of rarefied air and di rected again to the surface of the earth.