. Elements of radio telephony . quency than theblue, while having no visible effect on the eye, will affect aphotographic plate and produce other manifestations. Aswe go stiU higher we come upon the very short waves of highpenetrative power known as X-rays. These rays are invis-ible to the eye but are capable of affecting photographicplates and also produce luminous effects when impingingupon certain chemicals. Radio and light waves are identical except for the differ-,ence in frequency; it so happens that the human eye is sensi- EIGH-FBEQUENCY CURRENTS 9 tive to a rather restricted band of fr
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. Elements of radio telephony . quency than theblue, while having no visible effect on the eye, will affect aphotographic plate and produce other manifestations. Aswe go stiU higher we come upon the very short waves of highpenetrative power known as X-rays. These rays are invis-ible to the eye but are capable of affecting photographicplates and also produce luminous effects when impingingupon certain chemicals. Radio and light waves are identical except for the differ-,ence in frequency; it so happens that the human eye is sensi- EIGH-FBEQUENCY CURRENTS 9 tive to a rather restricted band of frequencies, otherwise wewould be able to see radio signals as flashes of hght. Radiotelegraph signals would be recognized as alternate flashes ofMght followed by periods of total darkness and radio tele-phone signals would correspond to the hght given off by alamp which flickered but never went out entirely. As willbe noticed there are several large bands almost entirelyunexplored and it is a matter of conjecture just what would. Damped Wave Fig. 5.—Sustained or continuous and damped waves. be found if radio receiving sets could be tuned to these par-ticular ranges. Damped and Sustained Waves.—There are two generaltypes of alternating currents useful in radio transmission,(a) those producing sustained waves and (6) those producingdamped waves. In the sustained type the currents vary between constantpositive and negative maximum values, each wave beingjust as high as its neighbor; while in the damped type thewaves become smaller and smaller as time goes on. For 10 ELEMENTS OF RADIO TELEPHONY instance, an organ pipe produces a sustained soiuid wavewhile a piano string produces a damped sound wave whichconstantly decreases in ampUtude. The difference betweenthese two types is illustrated in Fig. 5. Damped waves ingeneral are not of particular, interest in radio telephony,their principal appUcation being to radio telegraphy. There are several different schemes suitable for the p
