CHAFFEE. — IMPACT EXCITATION OF ELECTRIC OSCILLATIOxVS. 291 



There is obtained on the fluorescent screen by this arrangement a per- 

 fectly definite and well defined pattern, which gives the corresponding 

 instantaneous values of the primary and secondary currents. Plate 1 c, 

 is one of many photographs of such a pattern, taken with an exposuie 

 of about 15 to 30 seconds, and represents the conditions when adjust- 

 ments are made for maximum energy in the secondary circuit. 







Figure 13. 



Knowing, as will be adequately proved later, that the secondary 

 oscillation is sinusoidal, the primary current, plotted to time, and its 

 phase relation to the secondary current, can readily be derived from 

 the patterns mentioned above. In c of Plate 1 the vertical distance c/i 

 to the primary loop above, from any point on the horizontal line dis- 

 tant (5?2 from the center or undeflected spot, gives the instantaneous 

 primary current, ii, and the simultaneously secondary current, ?2- A 

 sine curve of amplitude represented by the secondary deflection is 

 drawn, and the time coordinate for any corresponding values of i^ and 

 12 is the time, obtained from the sine curve, at which the current 

 coordinate is i^- The direction of the spot of light is indicated by the 

 arrows. The curve marked ij, in Figure 14, shows the development of 

 two figures, both reduced to the same scale for better comparison. 

 In in the figure is the secondary current. Seven such developments 

 were made representing entirely different conditions, but in each case 

 the phase of A with respect to I2 was practically the same as is shown 

 in Figure 14, and the shapes of the /i curves differed so slightly that, 

 to save confusion, they are not reproduced. 



Examination of the photograph and of the developments show, as 

 was stated in Part I, that there is no inverse current. Although the 

 primary wave appears to have twice the period of the secondary oscil- 

 lation, if the slope of the curve, or — -^ which is proportional to the 



