Tide-predicting machine and voltaic pile: what they have in common

1. Step 1. Tide-predicting machine — uses — Fourier transform. A sum of harmonics.
2. Step 2. Fourier transform — is used in — Digital signal processor. Spectral processing.
3. Step 3. Digital signal processor — is part of — Modem. Signal processing in high-speed modems.
4. Step 4. Modem — is part of — Fax. It transmits an image over a telephone line.
5. Step 5. Fax — uses — Electrochemical reaction. The paper darkened under current.
6. Step 6. Electrochemical reaction — is used in — Voltaic pile. Current arises from the reaction of dissimilar metals with an electrolyte.

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