HISTORY OF ELECTRICAL RESONANCE 431 



transmitting aerial (an improvement credited to Ferdinand Braun of 

 Germany), and by means of a variable condenser in the former and a variable 

 inductance in the latter these two circuits could be tuned and brought into 

 resonance with each other. This accomplished the production of a much 

 more persistent train of oscillations in the aerial and a more efficient radia- 

 tion of energy. At the receiving end the aerial was tuned to the incoming 

 waves by means of a variable inductance, and the inductively coupled 

 detector circuit was in turn tuned to resonance, likewise by means of a 

 variable inductance. It was partly through such steps in the realization of 

 greater sensitivity as well as selectivity that Marconi eventually succeeded 

 with transoceanic telegraphy.* 



In this patent the inventor gave the specifications for nine different 

 tunes, as he called the different frequencies intended for different stations, 

 or for different distances; that is to say, the details of design of the aerials, 

 transformers, inductances and capacities of the transmitting and receiving 

 circuits for each tune. Thus interference between one station and another 

 might be avoided by using different frequencies. It may be observed here, 

 however, that the matter of selectivity was not so easy at that time when 

 the rather broad-spectrum spark transmitter was the only kind available. 

 Very sharp tuning had to wait upon the advent of continuous waves, 

 supplied first by the Poulsen arc or the high-frequency alternator and then 

 by the vacuum tube. But many other improvements, and new wonders 

 besides, were waiting on the vacuum tube. 



It hardly seems necessary to pursue our subject further than this point, 

 considering how it so quickly thereafter became a commonplace item in our 

 electrical storehouse. Our interest was chiefly in how it got started. We 

 have seen how it had its roots in certain experiments with the Leyden 

 jar; how the results of experiments were clarified by mathematical analysis 

 and a correct theory formulated; and then, as the need and opportunity 

 arose, how the principle was applied and made use of by inventive minds: 

 the wilderness first entered, then surveyed, and at last inhabited. So it 

 is, we find, with most new ideas in the scientific world. 



References 



1. Felix Savarj-, "Memoire sur rAimantation" ("Memoir on Magnetization"), Annates 

 de Chimie et de Physique, vol. 34, pp. 5-57, 1827. (Read before the Academy of 

 Sciences, Paris, July 31, 1826.) 



* Tesla's brilliant experiments with resonance and high-frequency currents during this 

 period and his knowledge and handling of tuned coupled circuits should be noted here. 

 Although his work for a time was concerned largely- with the conversion of ordinary power 

 source currents into currents of very high frequenc\' and voltage (his "Tcsla coil" of 1891 

 is still well known) for a proposed system of electric lighting by vacuum tube discharges, 

 much of it was applicable to wireless telegraphy. Particularly, his synchronous discharger 

 with adjustable electrodes and provision for tuning the low-frequency circuit to resonance, 

 patented in 1896, could very readily have been incorporated into a wireless transmitter. 



