744 



SCIENCE 



[N. S. Vol. XXXVI. No. 935 



have failed to take mucia interest in it. This 

 lack of interest is apparently due to the pre- 

 vailing prejudice against the claims of wire- 

 less telegraph companies in general. 



The system of wireless communication in 

 question is that invented by the Danish scien- 

 tist Valdemar Poulsen, and is radically dif- 

 ferent from the Marconi and related spark 

 systems. Instead of intermittent waves such 

 as are sent out by the spark system, the Poul- 

 sen system sends undamped continuous waves 

 by means of an arc. In transmitting a mes- 

 sage the signals are given not by interrupting 

 the current but by slightly varying the wave- 

 lengths in a continuous wave train. Experi- 

 ence is proving that such continuous wave 

 trains are far less affected by adverse atmos- 

 pheric conditions and other obstacles, and are 

 propagated long distances with much less 

 power than the broken waves sent out by the 

 spark system, and that they possess numerous 

 other advantages. As a result, entirely reli- 

 able communication for long distances over 

 land, and communication by day almost as 

 well as by night, is made possible. 



The greatest advances in the development 

 of this system are being made in the western 

 part of the United States, largely by persons 

 now or heretofore connected with Stanford 

 University. Stations ranging in power from 

 5 to 30 kilowatts are in operation in the large 

 cities on the Pacific Coast, from Seattle to 

 San Diego, and at Phoenix, El Paso, Fort 

 Worth, Kansas City and Chicago. Tele- 

 graphic messages are being transmitted con- 

 stantly, day and night, along the Pacific Coast 

 and as far east as El Paso, and messages are 

 sent from there by night to and from the com- 

 paratively low-power stations so far installed 

 at Fort Worth, Kansas City and Chicago. 

 Since the recent establishment of a 30-kilo- 

 watt station at San Francisco with two 440- 

 foot towers it has been found possible to send 

 messages direct from the coast to Fort Worth 

 and Kansas City, and do away with the inter- 

 mediate relays. Within the past few weeks a 

 station has been completed at Honolulu and 

 every day from 1,000 to 4,000 words of news 

 and private messages are sent thither by the 



San Francisco station. This news appears in 

 the Honolulu daily paper and, by virtue of its 

 cheaper cost than news by cable, is affording 

 the people there for the first time complete 

 news of the world each day. This distance is 

 more than 2,350 miles and is the longest over 

 which continuously successful wireless com- 

 munication has ever been established. 

 Furthermore it is the longest single span of 

 ocean necessary to cross in circling the globe, 

 and forecasts trans-Pacific wireless communi- 

 cation in the near future. The power used at 

 these Pacific coast stations is only a small 

 fraction of that necessary for sending mes- 

 sages by the spark system across the two 

 thousand miles of ocean from Ireland to Nova 

 Scotia. 



With the aid of mechanical transmitters 

 and receivers from 100 to 300 words per min- 

 ute are accurately sent and received by the 

 Poulsen system over distances of several hun- 

 dred miles, and a method has been devised 

 whereby two messages can be sent or two re- 

 ceived simultaneously over the same antenna. 

 The wave-lengths can be readily varied, and, 

 as each station has its assigned wave-length 

 to which it keeps its receiving apparatus at- 

 tuned, messages can be sent to any point de- 

 sired without troubling other stations. Or, if 

 desired, all stations within range can receive 

 the same message simultaneously. Messages 

 sent by the Poulsen system are not read by 

 operators of other systems and the stations do 

 not experience the interference from outside 

 operators which is so troublesome a feature of 

 the spark stations. 



In addition to telegraphic communication 

 the Poulsen system has been proved successful 

 for wireless telephony. I can personally at- 

 test the simplicity and clearness of this 

 method of transmitting speech, having tele- 

 phoned more than two years ago between 

 Stockton and San Francisco, a distance of 

 80 miles over land. Subsequently speech has 

 been carried in this way from San Francisco 

 to Los Angeles, 450 miles, but as yet no thor- 

 ough tests have been made of the system's 

 telephonic possibilities, attention having been 

 concentrated upon the telegraph. 



