Dynamic microphone and syringe: what they have in common

1. Step 1. Dynamic microphone — has part — Permanent magnet. The coil moves in the field of a magnet.
2. Step 2. Permanent magnet — is part of — Galvanometer. A magnet.
3. Step 3. Galvanometer — evolved into — Electrocardiograph. Einthoven’s string galvanometer.
4. Step 4. Electrocardiograph — is made of — Silver. The quartz string of Einthoven’s galvanometer is silvered.
5. Step 5. Silver — is material for — Syringe. Early needles were silver.

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