Quenched Spark Wein in 1906 discovered that very powerful discharges possessing advantageous properties for wireless telegraphy could be obtained from very short spark-gaps To avail of this discovery Von Lepel employed as an oscillation generator, a .device consisting of a metal box having a parti tion of two copper plates separated by a very thin sheet of paper provided with a small aper ture in its centre. The terminals of the usual charging electromotive force are each connected with one of the plates and the arc is formed at the small aperture between the plates, which arc slowiy burns away the paper which must be renewed at intervals. The arc is shunted by the usual inductance and capacity. This arrange ment produces very rapid quenching of the spark at the electrodes. Hence the primary oscillation circuit ceases to give out energy after the first blow, so to speak, while the secondary or aerial oscillation circuit continues to oscillate. It has been found in practice that with such rapidly damped primary oscillation circuits in coupled circuits, only one set of oscillations is radiated, whereas in less rapidly damped primary circuits the radiation of more than one set of radiations is not uncommon. Forms of quenched spark transmitters other than the Von Lepel arrangement have also been employed.
Electric Wave Meters.— It is very essential at times to measures the wave lengths or fre quencies of wireless telegraph circuits. For this purpose a number of wave meters have been devised. These wave meters are based primarily ,on the fact that with an exciting cur rent in proximity to a secondary circuit a maxi mum current will be induced in the secondary circuit when the two circuits are in resonance, which will be when they possess corresponding capacity and inductance. If the capacity and in ductance of the secondary are known, the fre quency and wave length are deducible. The period T of a complete electric oscillation varies with the inductance and capacity of the tircuit, according t,o the formula T =2/rV K L when T is the time in seconds, fr is the ratio of cir cumference to diameter, K is capacity in farads and L the inductance in Henrys—or T=62832 V K L. Hence it is evident that the frequency n of the oscillations (number per second) will be equal to I divided by T; that 1 is, n—. The velocity V of propagation of the oscillations or waves being equal to that of light waves, 186,000 miles per second, the wave length then equals velocity divided by frequency V —, or wave length equals,