Measurement of Peak Potential of Alternating Source. 301 



2. The application of the theory to the experimental 

 measurements is described. 



3, 4, 5. The experimental methods for tracing the wave- 

 form of the magneto are described. 



6. The values of the constants of a certain machine obtained 

 by these methods are given, and the values of the peak 

 potential calculated from them by the theory. The observed 

 values are very much less than those calculated. 



7. The damping of the oscillations is investigated. It is 

 shown that the main source of damping is one not contemplated 

 by the theory, namely, the losses in the iron core due to 

 hysteresis and eddy-cnrrents. 



8. The calculated peak potentials are corrected for the 

 observed damping and values obtained which, though in 

 much better agreement than before with the observed 

 values, are still considerably greater than the observed 

 values. 



9. Some further experiments in which the iron losses are 

 greatly reduced are described, but the same discrepancies as 

 before are noted. 



10. It is pointed out exactly in what points theory and 

 experiment agree and in what points they differ. It is 

 suggested that it is still possible that the theory may 

 provide a useful guide to design of magnetos, and the con- 

 siderations underlying the experiments to be described in a 

 second part of the paper are stated. 



XXY1. JSote on the Measurement of the Peak Potential of an 

 Alternating Source. By Clifford C. Paterson, M.I.E.E., 

 and Norman Campbell, Sc.D* 



THE method of measuring the peak potential of an alter- 

 nating source by means of a thermionic valve is now 

 familiar, but the conditions necessary for accuracy do not 

 seem always to be appreciated. 



Fig-. 1. 



A /v 



The connexions are shown in fig. 1. A is the source of 

 alternating potential, V the thermionic valve with its heating 



* Communicated by the Authors. 

 PUL Mag. S. 6. Vol. 37. No. 219. March 1919. Y 



