CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL LABORATORY, 



HARVARD UNIVERSITY. 



POSITIVE RAY'S. 



By John Trowbridge. 



Presented May 13, 1908. Received May 18, 1908. 



My intention in undertaking thi.s investigation was to endeavor to 

 measure the group velocity of the positive rays by producing a stand- 

 ing wave, or a stratum of maximum collisions in an exhausted tube in 

 the space between the anode and the cathode. In the case of an oscil- 

 lating circuit, if we call X the wave length, v the velocity of light, t the 

 time of a half oscillation, s the distance between the anode and the 

 cathode, v' the velocity of the positive rays, we have 



If, by tuning a circuit containing a condenser, self-induction, and 

 the exhausted tube, the strata of maximum collisions could be formed 

 at the orifice in the cathode, it was thought that none of the positive 

 rays would enter the canal region ; if, on the other hand, the positive 

 rays swung, so to speak, with the oscillations of the circuit, a maxi- 

 mum fluorescence could be obtained on a suitably placed willemite 

 screen. 



The circuit was arranged as follows : A Leyden jar, L, Figure 1, was 

 charged by a storage battery of ten thousand cells, through a large 

 resistance of running water, B. The discharging circuit included an 

 adjustable self-induction, I, a tube filled with rarefied hydrogen, T, 

 and a spark, S. K was an iron electrode, with an orifice two milli- 

 meters in diameter at its centre. A glass tube welded to the sides of 

 the tube C entered this orifice. The end of the tube C was coated 

 with willemite. 



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