Time & Measurement

Kelvin’s Tide-Predicting Machine as a Mechanical Harmonic Prediction Engine

Period and origin

Britain, from the 1870s; William Thomson, later Lord Kelvin

What it was built to do

To turn coefficients obtained from tidal analysis into a continuous curve of future tides.

How the mechanism works

A common time shaft drives one mechanism per constituent, each at its own angular rate. Adjustable radii encode amplitudes and initial crank angles encode phases; cords, chains, pulleys or summing linkages add the vertical components and move a pen.

Input

Amplitudes and phases for each tidal constituent, set on the machine.

Transformation

Physical parallel summation of sinusoidal basis functions driven from one time shaft.

Output

A drawn curve of predicted tide height against time.

What is evidenced

Established: the artefact or the documentary record carries this directly.

What it demonstrates

A physical parallel sum of basis functions - the principle that survives directly in Fourier synthesis, spectral modelling and model-based forecasting. It is a specialised analog computer, not a universal calculator.

All mechanisms