Best Primary Capacity for Tesla Coils

It has generally been assumed that to produce a maximum voltage on the secondary terminals the resonance relation L₁C₁=L₂C₂, as proposed by Drude, was sufficient, these symbols referring to the inductance and capacity of the primary and secondary respectively. Recently, however, Dr. Taylor Jones has shown that the above condition does not apply if the primary capacity alone is varied. If the coupling coefficient has the value k²=0·36, favoured by Drude, the best capacity is at least twice as great as the resonance value. Mr. W. Morris Jones, B. Sc., in an interesting communication to the “Philosophical Magazine,” has experimentally tested these results. With k²=0·348, this value nearly agreeing with that which Drude recommends, he found that the maximum was obtained with a ratio of 3·3L₁C₁=L₂C₂, and the primary capacity was much greater than for the resonance value given by the expression first referred to above. He also found that the experimental curve differed considerably from the theoretical curve.