. The principles underlying radio communication . oscillations could not be produced. The restoration ofthe non-conducting state is called quenching. A device calledthe quenched gap for very rapid quenching of the spark isdescribed below in this section. Additional appliances for theprevention of arcing are discussed in Section 167. Plain Gap.—A plain spark gap usually consists of two metalrods so arranged that their distance apart is closely adjustable. SPARK GAPS. 357 (See Fig. 182.) It is important that the gap be kept cool or itwill arc; for that reason the sparking surfaces should be ampl
. The principles underlying radio communication . oscillations could not be produced. The restoration ofthe non-conducting state is called quenching. A device calledthe quenched gap for very rapid quenching of the spark isdescribed below in this section. Additional appliances for theprevention of arcing are discussed in Section 167. Plain Gap.—A plain spark gap usually consists of two metalrods so arranged that their distance apart is closely adjustable. SPARK GAPS. 357 (See Fig. 182.) It is important that the gap be kept cool or itwill arc; for that reason the sparking surfaces should be the electrodes have fins for radiating away the heat. Anair blast across the gap will greatly aid the recharging by re-moving the ionized air, to which the conducting power of thegap is due. At the sparking surfaces an oxide slowly formswhich, being easily removed in the case of zinc or magnesium,is not very troublesome. With other metals in general theoxidation is serious and is rapid enough to make operationunstable and With a given condenser, the quantity of electricity stored onthe plates at each charging is proportional to the voltage im-pressed (Sec. 30), and this can be regulated by lengthening orshortening the spark gap to obtain a higher or lower voltage atthe beginning of the discharge. The length of the gap whichcan be employed is limited by the voltage that the transformeris capable of producing, the ability of the condenser dielectricto withstand the voltage, and the fact that for readable signalsthe spark discharge must be regular. If the gap is too long,sparks will not pass, or only at irregular intervals. The con-denser is endangered also. If the gap is too short it may arcand burn the electrodes. Arcing causes a short circuit of the 358 TRANSMITTING APPARATUS. transformer, and the heavy current that flows interferes withthe high-frequency oscillations. An arc gives a yellowish colorand is easily distinguished from the bluish white, snap
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