66 Mr. W. Morris Jones on the most Elective 



The method of taking a reading was as follows : — The tube 

 was first placed at a moderate distance from the secondary 

 terminal, and it was found that it glowed continuously over 

 a considerable range of values of the primary capacity. The 

 distance of the tube was then increased, the range of Ci 

 diminishing, until the tube failed to glow continuously but 

 flashed out only at the good primary discharges. By this 

 time the range of Ci was reduced to fairly narrow limits, 

 and the middle point of the range was taken as the optimum 

 primary capacity. The tube was further removed until these 

 isolated flashes just ceased to appear. The distance of the 

 tube from the terminal was then measured, and this distance 

 was taken as a measure of the maximum secondary potential 

 for the given degree of coupling and the given length of 

 spark-gap. 



The frequency-ratio of the electrieal oscillations of the 

 system, when so adjusted, was found by means of the wave- 

 meter. 



Period of the Primary Circuit. 



After the capacity had been adjusted to its most effective 

 value, the period of the primary circuit was determined. 

 This was done by means of a " dummy " primary. This coil 

 was similar in all respects to the primary of the Tesla coil. 

 It had the same number of turns and was made of the same 

 wire. The turns were also of the same diameter as those on 

 the primary, and both coils gave the same reading on the 

 wavemeter when connected up respectively to a constant 

 •capacity and spark-gap. 



The reading obtained with the wavemeter when the 

 " dummy " had been substituted for the primary of the 

 Tesla coil, gave I^Ci. 



Determination of k 2 and L 2 C 2 . 



The coupling coefficient of the primary and secondary 

 •circuits was next found The "dummy" primary coil 

 having been substituted for the primary of the Tesla coil, 

 and the latter removed to a distance of two or three feet, the 

 primary capacity was varied until the circuit came into tune 

 with the secondary, resonance being indicated by the glow 

 of a neon tube attached for the purpose to the lower secon- 

 dary terminal. By removing the Tesla coil to a sufficient 

 distance, the range of the capacity in the " dummy " circuit 

 over which the tube glowed could be cut down to very 

 narrow limits, and the "dummy" circuit adjusted fairly 

 accurately to resonance with the secondary. This tuning 



