694 



Dr. J. A. Fleming on Magnetic Oscillators 



They show how much the receiver current varies with the 

 height of the coils above the ground, the maximum value 

 being reached when the coils are about 2 inches above the 

 surface. Also they show that when the coils are laid flat on 

 the ground there is a great increase in the power taken up 

 by the arc. 



Raising the coils from 6 inches to 6 feet above the ground 

 decreased the secondary currents to one-fifth. 



Exp. VIII. Comparison of coils of different areas. — The 

 two large or 8-feet coils were compared with the two small 

 or 2-feet coils. In both cases the distance between primary 

 and secondary was 79 feet, and the coils were parallel to the 

 earth and at 6 inches above the surface. In both cases the 

 primary current was 5*4 amperes. 



The small coils had 8 turns and were tuned to a frequency 

 of 214,400. 



The large coils had 5 turns and were tuned to a frequency 

 of 162,000. 



Table VIII. 



Coils used. 



Number 



Of tlUUlS. 



Secondary 

 Frequency. Current in 

 milliamperes. 



Small. 



2 feet in side ... 



Large. 



8 feet in side . . . 



8 

 5 



214,400 

 162,000 



0-082 

 27'4 



The large coil therefore produces 340 times the effect of 

 the small coil. 



Exp. IX. Comparison of the same coils ivith different 

 numbers of turns. — The two large coils were wound with 

 two circuits each of 5 turns and they could be joined in 

 series so as to make a coil of 10 turns. The coils were placed 

 parallel to the earth and at a distance of 6 inches above it. 

 The primary current used in both cases was 5*4 amperes. 

 The inductance of the primary circuit was 380,000 cms., and 

 when 10 turns were used it was 1,000,000 cms. The power 

 taken up in the arc therefore was not the same in the two 

 cases. 



