This change in frequency is achieved by varying the electrical capacitance in the tuned circuit of the oscillator.
"LRL Accelerators The 184-Inch Synchrocyclotron"
Lawrence Radiation Laboratory
As the blades of the tuning forks vibrate, the capacitance is alternately increased and decreased by the required amount.
"LRL Accelerators The 184-Inch Synchrocyclotron"
Lawrence Radiation Laboratory
A fixed condenser of the exact capacitance required for connecting across the head phones is mounted in a base fitted with binding posts, as shown at B, and costs 75 cents.
"The Radio Amateur's Hand Book"
A. Frederick Collins