Lodestone and pneumatic tube: what they have in common

1. Step 1. Lodestone — uses — Magnetism. A natural magnet.
2. Step 2. Magnetism — is used in — Hall sensor. It responds to a magnetic field.
3. Step 3. Hall sensor — is part of — Anti-lock braking system (ABS). Sensors measure the wheel speed.
4. Step 4. Anti-lock braking system (ABS) — evolved from — Air brake. Anti-skid systems first appeared in aviation and on railways.
5. Step 5. Air brake — uses — Compressed air. The brake is controlled by air pressure in the train pipe.
6. Step 6. Compressed air — is used in — Pneumatic tube. Air pressure.

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