WIKELESS TELEPHONY PESSENDEN. 



171 



was made use of in 1898 for the piui)Ose of producing prolonged 

 trains of sustained waves. 



Various types of connection between the antenna and the local 

 oscillatory circuit were tested, but it was found that the most efficient 

 results Avere obtained by connecting the local circuit directly across 

 the spark-gap." 



The results of some comparative tests are here given. The figures 

 in the column " A " are for the local circuit connected directly to the 

 terminals of the spark-gap, those in column " B " are for an auto- 

 transformer, those in column " C " for a loose-coupled primary and 

 secondary. 



Frequency 



Tank capacity (m. f.) ... 

 Kilowatt output dynamo 

 Tank current (amperes) 

 Antenna current 



212, 000 



0.072 



30 



300 



48 



The large station at Brant Eock is operated with the local circuit 

 directly connected across the spark-gap, partly because the efficiencj'^ 

 is somewhat greater, but also on account of the great simplification of 

 connections and the fact that the degree of sustainment of the wave 

 train may be adjusted very simply, if desired, by sliding the lower 

 terminal of the antenna along a few inches of the lead of the local 

 oscillatory circuit. 



Cooper-Hewitt '^ in 1902 used a modification of his mercury lamp 

 to obtain intermittent discharges, each followed by a train of high- 

 frequency oscillations. 



Arc methods. — The worker with high-frequency oscillatory cur- 

 rents will soon discover that we are indebted to the genius of Prof. 

 Elihu Thomson for practically every device of any importance in 

 this art. 



The method of producing high frequency oscillations from an arc 

 and continuous current was discovered by him in 1892.^^ Figure 1, 

 taken from his patent, shows the general form of his arrangement. 

 If the directions given in the specification are folloAved no difficulty 

 will be met with in obtaining frequencies as high as 50,000 per second. 



Between 1900 and 1902 some experiments were carried out with 

 the Elihu Thomson arc as a source of high frequency oscillations for 

 wireless telegraphy and telephony. 



o United States patents Nos. 706735 and 70G73G, December W, 1S99. 

 6 Cooper-Hewitt, United States patent No. 780999, April 25, 1902. 

 c Elihu Thomson, United States patent No. 500030, July 18, 1892. 



