An oscillograph has been designed and constructed which will reproduce in ink on paper tape the wave form of steady state a.c. voltages or currents in the frequency range 50 to 25,000 cycles. The tracing is done at a speed of approximately 1 cycle in 3 seconds, and represents a recording of the instantaneous voltage or current progressively at different phase positions in the cycle. The principle of the device is that of the Rosa curve tracer, but operation has been made automatic by the

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... ction of several new features, including an electrical phase shifter, a new type of electronic switch, and a recording milliammeter. The sources of error in the apparatus are analyzed and are shown to be reasonably small in magnitude and the error capable of further reduction. An appendix describes the use of the instrument as an harmonic analyzer.