692 



Dr. J. A. Fleming on Magnetic Oscillators 



The results of the last two experiments is to show that 

 for constant primary current the receiver current is a 

 maximum for a certain height of the coils above the earth's 

 surface. The observations are delineated in fig. 7. 



Fi< 



0-6 



coil in *feet 



It is obvious, however, that all the measurements in which 

 the coiis are placed horizontal and at varying heights above 

 the ground need caution in interpreting them. When the 

 coil is placed with its plane parallel to the earthy currents 

 must be induced in the soil, and the effective inductance of 

 the coil and therefore the frequency of the current must 

 be altered. The nearer the ground the less is the effective 

 inductance of the coil, but on the other hand the capacity is 

 increased. Hence, even if the primary high-pressure current 

 is kept constant, there will be variations of frequency which 

 affect the inductive action of the primary on the secondary. 

 That such is the case was shown by the results of a further 

 set of measurements with the large coils, the power taken up 

 in the arc and its power-factor being observed at the same 

 time. 



