CHAFFEE. — IMPACT EXCITATION OF ELECTRIC OSCILLATIONS. 287 



It i3 thought that the variation of frequency with changing supply- 

 current is due to a wavering or shifting of the period of the secondary 

 oscillation between a forced condition, when the primary is in action, 

 and the free period of the secondary circuit, when unaffected by the 

 primary discharge, this wavering being more often and of a greater 

 effect on the resultant or average w^ave length the greater the number 

 of primary discharges per second. The number of primary discharges 

 is proportional to the supply current, so that according to the above 

 assumption, the change in frequency would be directly proportional to 

 the supply current. 



The large changes in frequency with changing arc current and arc 

 length is a serious disadvantage in the use of the Poulsen arc, but 

 with the system being studied, the change of frequency is so small and 

 the supply current and arc length remain so very constant that there 

 is, under all ordinary circumstances, practically no change in frequency. 



Part II. 



Analysis of Oscillations by Means of Braun Tube' 



Oscillographs. 



In Part I the general characteristics of the aluminum-cathode oscil- 

 lation gap were studied, but little idea could be obtained as to the 

 instantaneous relations of the variables. It is the purpose in Part II to 

 analyse, by means of the Braun cathode-ray tube, the entire sequence 

 of events during a complete cycle of changes, and to develop a clearer 

 idea of the nature of the oscillations and the action of the gap. Before 

 attacking the problem, however, it is necessary to describe the additional 

 apparatus made use of in the following experiments : 



(1) The Braun Tubes and Accessory Apparatus. 



The Braun cathode-ray tube is a most valuable piece of apparatus 

 for delineating transient electrical phenomena. Its use has been de- 

 scribed by Braun,® Zenneck,^ and others,^ but a few words from the 

 author's experience with the use of the Braun tube in connection with 

 high frequency currents may be of interest. 



The Braun tubes used in the following work were imported from 

 Germany, but it was found necessary to alter them. The aluminum 



6 F. Braun, Wied. Ann., 60, 5.52 (1897) ; Elektrot. Ztschr., 19, 201 (1898). 

 ' Zenneck, Ann. d. Physik., 9, 497 (1902). 



8 .1. M. Varley, Phil. Mas;., 3, 500 (1902) ; Varley and Murdock, Elec- 

 trician (London), 55, 335 (1905). 



