Decembee 13, 1907] 



SCIENCE 



823 



oscillations are maintained eontinuously of 

 unvarying amplitude. 



With the arc method we are further able 

 to choose the number of consecutive oscilla- 

 tions which make up each signal sufficiently 

 great to obtain the very best syntony. On 

 the other hand, improvement in the ar- 

 rangement and construction of the appa- 

 ratus for the spark method has so increased 

 the number of oscillations corresponding 

 with each spark that it may be that we 

 shall be able to obtain a sufficient number 

 in each train to give as good syntony by 

 this method as that obtained with the arc 

 method. 



The arc method seems eminently suitable 

 for very high speeds of working. As the 

 oscillations are quite continuous, we can 

 cut them up into groups to form the dots 

 and dashes of the Morse alphabet, just as 

 if we were working with a continuous cur- 

 rent such as is used on land lines, so that 

 there seems no reason why as high a speed 

 of working should not be obtained from the 

 arc method of wireless telegraphy as is ob- 

 tainable by automatic signalling on land 

 lines ; for it is to be noted that the dot or 

 shortest signal of the Morse alphabet, even 

 at a speed of three or four hundred words 

 per minute, will last long enough to consist 

 of many hundreds of oscillations of the 

 current in the aerial, so that there will be 

 plenty of oscillations in the group forming 

 the dot to give good syntony. 



Turning to the spark method for high 

 working speeds, we find a difficulty in that 

 the dot of the Morse alphabet must at least 

 occupy the average time required to charge 

 the condenser or aerial and produce one 

 spark, and preferably sufficiently long for 

 several. We are therefore obliged in the 

 spark method to use a high rate of spark- 

 ing for high-speed signaling. This diffi- 

 culty has not become very serious with the 

 present low speeds of sending. When we 

 come to use considerable amounts of power 



to transmit messages over long distances, 

 and we also require a high speed of work- 

 ing, the practical difficulty in constructing 

 apparatus suitable for sufficiently rapid 

 sparking vnll become serious. 



Mr. Marconi in 1905 claimed to have 

 already reached a speed of 100 words per 

 minute by the spark method, and lately 

 there has appeared in the technical press 

 examples of high-speed signaling by the 

 British Post-office over a distance of fifteen 

 miles in which readable signals were re- 

 ceived at a speed of seventy words per 

 minute. 



Turning to the receiving end, almost all 

 the receivers that have been used in the 

 spark method can be equally well used for 

 the arc method ; for it must be remembered 

 that the transmission in either case is 

 affected by Hertzian waves traversing 

 space, and that the only fundamental dif- 

 ference consists in the number of oscilla- 

 tions in each train of waves. It must be 

 noted, however, that in those methods in 

 which a telephone receiver is used it is 

 necessary to break up the continuous oscil- 

 lations of the arc method into groups suc- 

 ceeding one another sufficiently rapidly to 

 produce an audible sound in the receiver; 

 for in the spark method the sounds we hear 

 in the receiver correspond with the succes- 

 sion of impulses of the diagram, one for 

 each spark at the transmitter. This chop- 

 ping up of the continuous wave-train so 

 as to produce audible signals in the receiv- 

 ing apparatus can be done either at the 

 transmitting end or in the receiving ap- 

 paratus. An example of this latter method 

 is Poulsen's ticker. 



The question whether receiving appa- 

 ratus can be arranged so as to receive mes- 

 sages from stations equipped with the spark 

 apparatus and from stations equipped 

 with the arc apparatus is a matter of 

 enormous importance at the present mo- 

 ment in view of the probable ratification of 



