HISTORY OF Kl.ECTRICAl. RESONANCE 427 



tf)()l, or technique, that is now cjuite faniihar in electrical laboratories. He 

 made use of this in the study of the harmonics generated in a circuit by the 

 magnetic reactions of an iron core upon the magnetizing current, an effect 

 that had been observed and for the hrst time correctly explained by Rowland 

 at Johns Hopkins, and a description of his method was published in 1893."'" 

 The following year, yielding to the suggestions of his scientific friends, 

 according to the account he has written ('T often regretted it, because it 

 involved me iji a most expensive and otherwise annoying legal contest"-'), 

 he made application for a patent on "Multiple Telegraphy", applying this 

 idea of selecting b}' resonance to the problem of separating the signals. -'- 

 Very soon afterwards another inventor, John Stone Stone, appeared upon 

 the scene with practically the same idea,-'^ and interference cases thereupon 

 resulted in the U. S. Patent Oflllce and the courts involving these two and the 

 French inventors ITutin and Leblanc, who had also tiled in the United 

 States."'* Upon the claims of the contestants and the differences that 

 characterized their schemes for multiplex signaling we need not dwell; 

 suffice it to say that in the matter of priority Pupin w^as adjudged the 

 winner.* It appears that this distinguished scientist was not unim- 

 pressed with what he considered the originality of his ideas about the 

 practical use of resonance. In the inimitable story of his life, "From 

 Immigrant to Inventor," he refers to this as "my invention of electrical 

 tuning,"-^ and says again, "I called it electrical tuning, a term which has 

 been generally adopted in wireless telegraphy."-'^ In another place, and on 

 another occasion, he said, "It was badly needed and I had it developed 

 several years before Marconi had made his invention. . ."-^ 



Before passing to other applications in the field of electric communication, 

 chiefly in the radio art, it might be said that in these early proposals for 

 multiplex operation the separation of the carrier frequencies could not be 

 successfully achieved by so simple a means as an ordinary resonant circuit. 

 For one thing, the listortion introduced would be prohibitive, unless the 

 carrier channels were placed so far apart as to be uneconomic. It remained 

 for the Campbell band filter, invented about twenty years later, to enable 

 the frequencies to be squeezed close together and distortion and other 

 difficulties to be overcome. Furthermore, the whole art had to wait for the 

 invention of the vacuum tube as the perfect generator of the kind of currents 

 required, as well as modulator, amplifier and demodulator of these currents. 



Later developments in the intricate and complex technique of wire 



* An examination of the report of the interference hearings (reference 24) shows 

 that Pupin claimed to have conceived the idea of using electrical resonance in multiplex 

 telegraph)- in the summer of 1890, following a careful stud>- he had made of the investiga- 

 tions of Hertz, and to have begun experimL'ntal work on it in October of that year, thus 

 antedating Hutin and Leblanc. Upon the adjudication of this contest in favor of Pupin 

 on the main issues, patents on some of their claims were also allowed Stone and the French 

 inventors. 



