302 PROCEEDINGS OF THE AMERICAN ACADEMY. 



shape with the experimental curves (heavy lines). The scales of the 

 curves serve only to give an approximate idea of the magnitudes of the 

 resistances at different cun-ents, for the position of the curves depends 

 upon the arc length and undoubtedly upon the period of discharge. It 

 is -worthy of note that the resistance at zero current is very high, thus 

 admitting of a high initial charge in the primary condenser before the 

 gap breaks down. The resistance curves are very steep, being much 

 steeper than the corresponding curves for the Poulsen arc. It is, in 

 part, this steepness which adapts the gap to the production of very high 

 frequency oscillations. The very rapid reestablishment of the high 

 resistance is also of primary importance in the action of the gap with 

 high frequencies. 



The upper dot-and-dash curve is for the curved point at the end of 

 the potential deflection in cut e of Plate 3 just mentioned, and repre- 

 sents the conditions for glow discharge. 



(4) The Inverse Charge Frequency (I. C. F.). 



Reference has often been made to the I. C. F., the value of which, as 

 was stated, depends upon the wave length of the secondary oscillation, 

 the size of the primary condenser (7i, and the value of the supply cur- 

 rent Iq. In order to show that the I. C. F. has, under most conditions, 

 a perfectly definite value, and at the same time, to illustrate some other 

 points concerning the system, the photographs of Plate 4 were taken. 



The arrangement of circuits, for the figures under discussion, was as 

 follows : Two parallel deflecting coils were placed about the Braun 

 tube, and so situated as to deviate the cathode beam in a direction 

 perpendicular to the electrostatic deflection. One of these coils was 

 connected in the primary circuit and the other in the secondary 

 circuit. The electrostatic deflecting plates were connected to the 

 terminals of the primary condenser C^. 



The oscillograms of Plate 4 represent, therefore, the sum of the 

 primary and secondary currents by deflections in the vertical direction, 

 and the potential of Ci, by deflections in the horizontal direction. In 

 all of the cuts the straight lower portion results fi'om the secondary 

 oscillation during the charging of Ci, when the gap current is zero. 



The explanation of cut h will serve for all of the pictures of Plate 4. 

 At point A the condenser Ci is charged to a potential sufficient to 

 jump across the gap. When the primary discharge begins, the spot of 

 light moves very rapidly at first over the loop A EC. This discharge 

 starts or maintains the secondary oscillation, so that the vertical deflec- 

 tion is due to the primary current plus the simultaneous secondary 



