 John Bertrand Johnson

John Bertrand Johnson was an electrical engineer whose 1928 measurements established the thermal electrical fluctuations now called Johnson-Nyquist noise. He detected random voltage fluctuations in conductors through a vacuum-tube amplifier and a thermocouple, and related the measured effect to temperature, electrical resistance and the measurement system's frequency response.^[ref]

This reveals why the average voltage alone is not enough to characterize a fluctuating signal. Its expected value can vanish while its mean-square value is positive. The fluctuations become an experimentally measurable noise floor in sensitive electronics, and their temperature dependence connects circuit measurements with the Boltzmann constant.^[ref]