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HISTORICAL DRAWING · 1876

Liquid transmitter

How large is a static current change from a resistance perturbation?

Alexander Graham Bell's lab notebook, pp. 40–41, March 10, 1876: liquid transmitter sketch and the "Mr. Watson — Come here" entry
Alexander Graham Bell's lab notebook, pp. 40–41, March 10, 1876: liquid transmitter sketch and the "Mr. Watson — Come here" entry. View the original source and attribution ↗

A contemporary sketch model

Every number below is a modern illustrative assumption. The historical drawing supplies a question; the source model is an exercise in reasoning about it.

voltage = 3 V "Illustrative bench supply"
seriesResistance = 100 ohm
transmitterResistance = 200 ohm "Illustrative nominal liquid-contact resistance"
deltaResistance = 10 ohm in 1..30 "Small imposed resistance change"
baseline := voltage/(seriesResistance+transmitterResistance) [A]
perturbed := voltage/(seriesResistance+transmitterResistance+deltaResistance) [A]
signalChange := abs(perturbed-baseline) [mA]
check measurable: signalChange >= 0.2 mA
sweep Contact: deltaResistance = 1, 10, 30 ohm

Model limits

A pair of DC points; no acoustics, diaphragm motion, waveform, intelligibility or transient circuit simulation.

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Create a Study, inspect the installed capabilities, and use this source as a starting point. Ask the agent to explain the equations and assumptions, then replace illustrative inputs with measured evidence for your own design.

This example includes a scalar sweep. Use napkin_sketch to add the model and napkin_run to inspect the sweep; the source editor’s scalar comparison view is for simple scenarios.

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