= Bloch nuclear induction experiment
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In their 1946 letter, <Felix Bloch>, <William Webster Hansen>, and <Martin Packard> reported <water> at room <temperature>. A steady <magnetic field> along $z$ and an oscillating field along $x$ produced a <signal> in a pickup coil along $y$, displayed on an <oscilloscope>. Some samples included paramagnetic additives to accelerate <thermal equilibrium>. Resonance fields at two <frequencies> gave the same field-to-frequency ratio, consistent with the <proton> value.<Nuclear Induction by Felix Bloch and others>[p. 127, Nuclear Induction, entire letter; geometry, water, additives, readout and two-frequency check]{ref}
The detailed paper describes glass <water> bulbs inside tuned receiving coils. Transmitter coils, shields and a conducting paddle controlled leakage. Field modulation at 60 Hz drove the horizontal <oscilloscope> sweep. A <diode> and audio amplification supplied the vertical trace. Vibration changed coupling: their largest difficulty. Coil tuning capacitors formed tank circuits. The actual receiver omitted the conceptual diagram's radiofrequency <amplifier>.<The Nuclear Induction Experiment by Felix Bloch and others>[pp. 475–480, Figs. 1–4, APPARATUS and opening RESULTS; actual diode receiver versus conceptual amplifier]{ref}
The orthogonal coil axes suppress direct transmitter pickup, but do not eliminate it. A field-dependent <signal> at the nuclear resonance must be distinguished from leakage and <noise>; merely detecting a radiofrequency voltage is insufficient. This is why the field sweep and the independently checked field-to-frequency ratio matter.
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