390 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



crackling sound it emitted ; or, better, the proper vacuum could be de- 

 termined by using the bulb as interrupter for a Tesla coil during the 

 exhaustion. 



Figure II is a diagram of the arrangement of the circuits as they are 

 employed with the Tesla coil. C is a condenser charged from the sec- 

 ondary of a step-up transformer P S actuated by the 110-volt alternating 

 light circuit. At intervals this condenser discharges through the inter- 

 rupter I and through the primary P' of the Tesla coil, as follows : 

 When the potential of C becomes high enough to start the discharge, the 

 resistance of the interrupter drops to a fraction of an ohm, and the elec- 

 tricity from the condenser surges back and forth through C P' I. These 



Figure II. 



rapid oscillations in the primary of the Tesla coil induce high potentials 

 in the secondary S'. When the current density through the interrupter 

 becomes small, the bulb ceases to be conducting, the condensers are again 

 charged by the transformer P S, aud the series of oscillations is repeated. 

 To get good results the secondary S' of the Tesla coil must be in reso- 

 nance with the primary circuit C P'. With the Cooper Hewitt inter- 

 rupter at I the Tesla coil gives a much longer and a much more uniform 

 discharge than when a zinc or an iridium spark-gap is employed as 

 interrupter. 



In one form of wireless telegraph circuit first suggested by Braun * and 



* F. Braun, Pliys. Zeit., 3, 143 (1901). Drahtlose Telegraphie durch Wasser 

 und Luft, Leipzig, 1901. Simon and Reich, Phys. Zeit., 4, 365 (1903). M. Wien, 

 Ann. der Phys., 3, 686 (1902). 



See also the controversy between Braun and Slaby as to priority, in various 

 recent numbers of Ann. der Physik. 



