1892.] Mr. Nikola Tesla on Alternate Currents, dx. 637 



EXTEA EVENING MEETING, 



Thursday, February 4, 1892. 



Sir Feedeeick Bramwell, BarL D.C.L. F.R.S. Honorary 

 Secretary and Vice-President, in the Chair. 



Nikola Tesla, Esq. 



Alternate Currents of High Potential and High Frequency, 



At the first outset this investigation was taken up with the view 

 of studying the effects of rapidly changing electrostatic and electro- 

 magnetic stresses. It was thought, from theoretical considerations, 

 that some useful observations would be made in following up this 

 line of experiment by means of properly constructed apparatus ; bat 

 the anticipations were by far surpassed, for a number of unexpected 

 phenomena were noted, and some novel facts brought to light, which 

 Iiave opened up a new and promising field of research. Some of the 

 results obtained are of special interest on account of their direct 

 bearing upon the problem of producing an efficient illuminant 



The phenomena which are due to the changing character of the 

 stresses are exalted when the time rate of change is increased, hence 

 the study of these phenomena is much facilitated by the employment 

 of apparatus adapted especially for the purpose of carrying on such 

 investigations. With this object in view, several types of alternators 

 were constructed, capable of giving currents of frequencies from five 

 to ten thousand and even more. Currents of much higher frequencies 

 used in some of these experiments, were obtained by disrupt! vely 

 discharging condensers. 



The construction of the alternators offered at first great difficulties. 

 To obtain these frequencies it was necessary to provide several 

 hundred polar projections, which were necessarily small and offered 

 many drawbacks, and this the more as exceedingly high peripheral 

 speeds had to be resorted to. In some of the first machines both 

 armature and field had polar projection^. These machines produced 

 a curious noise, especially when the armature was started from the 

 state of rest, the field being charged. The most efficient machine was 

 found to be one with a drum armature, the iron body of which con- 

 sisted of very thin wire annealed with special care. It was, of course, 

 desirable to avoid the employment of iron in the armature, and several 

 machines of this kind, with moving or stationary conductors, were 

 constructed, but the results obtained were not quite satisfactory, on 

 account of the great mechanical and other difficulties encountered. 

 A few of the machines constructed were described in some periodicals 

 of the past year, notably in the Electrical Engineer, New York, 

 March 18, 1891. 



