304 PROCEEDINGS OF THE AMERICAN ACADEirT. 



necessary to drive the mirror by some synchronous device so that the 

 image of the developed figure may be stationary on the photographic 

 plate for a time sufficient to make the exposure. This synchronizing 

 device is not difficult to arrange when using commercial alternating 

 currents, but when it is desired to take an oscillogram of a high 

 frequency current or condenser discharge, it is usually impossible to 

 make the necessary synchronization. When using high frequency 

 currents, the velocity of the spot of light on the fluorescent screen is 

 so great that, in order to obtain a photograph, it is necessary that the 

 cycle of changes, as shown by the pattern on the screen, be repeated 

 many hundred thousand times with such regularity and certainty that 

 the image is always in exactly the same position. The requirements 

 of both the acting system and the synchronizing device are very 

 exacting. 



The development of the time axis can be most effectually accom- 

 plished with the system under discussion by the very simple connection 

 which was used in the last section. The electrostatic plates, which 

 cause a deflection perpendicular to the current coils, are connected to 

 the terminals of the primary condenser C i. During the interval be- 

 tween primary discharges, when the primary condenser is charging, the 

 primary current is zero, and the main or charging current is almost 

 perfectly constant on account of the large inductances in the mains. 

 This uniform charging causes a uniform increase in potential of the 

 condenser d, and' hence a uniformly developed time axis on the fluor- 

 escent screen. The oscillations of the secondary, or any effect started 

 by the primary discharge, is thereby developed, as is shown by the 

 lower portions of the cuts of Plate 4. 



This arrangement for the development of current or potential de- 

 flection with respect to time is of the greatest use in many ways. Its 

 application will be illustrated here by showing the damping curves 

 with oscillations of a frequency of two million or more per second. 



Cuts a and h of Plate 5 represent the damping of the secondary 

 oscillations due to the addition of resistance in the secondary circuit. 

 The primary capacity and supply current were so adjusted as to give 

 large values of the I. C. F. in order that as many secondary oscilla- 

 tions as possible might appear in the damped oscillation trains shown. 

 The adjustments for the pictures of Plate 6 were so made that each 

 oscillation train is just completed before the beginning of the next. 

 The trains, therefore, succeed each other with no intervals of rest. By 

 adjustments of the supply current or primary capacity it is possible to 

 lengthen or shorten the interval between the primary discharges, and 

 by varying the resistance in the secondary circuit the number of oscilla- 



