2 BELL SYSTEM TECHNICAL JOURNAL 



that vision as well as speech may be carried long distances overland. It 

 does not require a bold stretch of the imagination to predict that some day 

 we shall have multiple-channel transmission of television as today we have 

 multiple-channel transmission of speech. Conductors consisting of hollow 

 pipes ofifer promise of such application. 



Indeed, frequency band width has become almost a commodity to the 

 communication engineer. Telegraphy takes a certain band width as meas- 

 ured in cycles per second for a particular speed of signaling as measured 

 in words per minute. We may assign about 100 cycles to a printing tele- 

 graph machine that prints 60 words per minute. To get intelligible tele- 

 phone communication requires about 1000 cycles, though Bell's original 

 instrument probably used effectively somewhat less than that, which 

 accounts for Kelvin's dilhculty in understanding certain words over it. 

 Commercial telephony has benefited from a gradually widened frequency 

 band, until now we look on 3000 cycles as a reasonable engineering standard. 

 This does not provide, however, for perfect transmission of speech. The 

 frequencies in speech commonly cover about 8000 cycles, though frequencies 

 above 4000 contribute little to either intelligibility or quality. Music 

 requires more band width than speech. The range of the normal human 

 ear is about 15,000 cycles, and perfect transmission of music requires that 

 band width. In practice, however, one loses little of esthetic value if the 

 music is limited to 8000 cycles. In fact, most listeners cannot readily 

 distinguish music transmitted over an 8000-cycle band from that over a 

 15,000-cycle band. Television requires from 20,000 cycles for a recognizable 

 human face, to 20,000,000 or more for vision as well defined as in standard 

 cinema practice, but in present commercial practice the band width is 

 limited to about 3,000,000 cycles. 



With a transmission line of given band width, we can allocate its avail- 

 able frequency range to telegraphy, telephony or television as we will. 

 Twenty printing telegraph channels with adequate separation cost in fre- 

 quencies about as much as one ordinary telephone channel, but for a tele- 

 vision channel we must pay the price, in frequencies, of 1000 telephone or 

 20,000 printing telegraph channels. 



It is of the extension of the range of frequencies and their availability 

 for transoceanic communication and particularly transatlantic telephony 

 that I wish to speak. We shall first review what have been the conse- 

 quences of the extension of frequencies and then explore some of the future 

 possibilities of further expansion of band width in transoceanic communica- 

 tion. Both radio and wire systems must be included to make the picture 

 complete. 



The first messages to cross the transatlantic cable were sent at the rate 

 of two words per minute. In frequencies, this means a band width of less 



