Section III
Compensation
Metal changes length with heat.
Metal changes length with heat, so a pendulum keeps a different second in July than in January. The answers were mechanical before they were metallurgical: rods working against each other, a jar of mercury, a split balance rim, and eventually an alloy that hardly moves.
3 entries
Each one a mechanism and the error it defeats- 01
The gridiron
Alternating brass and steel rods expand against each other so the pendulum's length stays put.
- 02
Mercury and invar
A jar of mercury rising as the rod lengthens, and later an alloy that barely moves at all.
- 03
The bimetallic balance
A split rim of two metals curls with temperature and moves the mass inward.
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