172 



ANNUAL REPOET SMITHSONIAN INSTITUTION, 1908. 



Some difficulties were found, for example, the arc could not be 

 started and stopped as quickly as was necessary for telegraphic pur- 

 poses, and the intensity of the oscillations and their frequency varied 

 considerably. These were overcome by making some minor improve- 

 ments, for example, the difficulty in sending was overcome by per- 

 mitting the arc to run continuously and using the key to change the 

 electrical constants of the circuits.'^ The difficulty in keeping the 

 intensity and frequency constant was overcome by substituting re- 



sistance for a portion of 



the inductance, and also 

 by using the arc under 

 pressure,^ 



Tests made by Doctor 

 Austin ^ show that Avith 

 this method frequencies 

 as high as 3,000,000 per 

 second and efficiencies 

 as high as 60 per cent 

 can be obtained together 

 with an absolutely 

 steady ^ generation of 

 the high frequency cur- 

 rents and an absence of 

 harmonic frequencies. 



High frequency alter- 

 nator. — The first high 

 frequency alternator 

 was built by Prof. Eliliu 

 Thomson in 1889. And 

 it^ was while experi- 

 menting with it in 1900 that Doctor Tatum made his very in- 

 teresting discovery that high frequency currents of large amperage 

 could be passed through the body without injury.^ 



« United States patents Nos. 706742, July 6, 1902 ; 706747, September 28, 1901 ; 

 727330, March 21, 1903 ; 730753, April 9, 1903. 



6 Ibid and United States patent No. 706741. 



" Austin, Bulletin of the Bureau of Standards, vol. 3, No. 2. 



^Austin assumed from the figure he obtained for the* dampening, that the 

 oscillations were not contiiuious ; but the method used for determining the 

 dampening is not applicable to this case, and a comparison of the currents 

 and voltages with the frequencies given in Austin's experiments, shows that 

 these oscillations must have been continuous. 



" Thomson, Electrical Engineer, July 30, 1890, and London Electrician, Sep- 

 tember 12, 1890. 



f Thomson, Electrical Engineer, March 11, 1891. 



Fig. 



1. — Eliliu Thomson's method of producinji 

 high frequency oscillations. 



