Section IV
Free Pendulum
Stop touching it.
By this point friction and heat were largely beaten. What remained was the impulse itself: every push and every count disturbs the thing being measured. The answer was to split the clock in two and leave one half alone.
3 entries
Each one a mechanism and the error it defeats- 01
The Shortt free pendulum
Two pendulums, one doing nothing but swinging in vacuum while a slave does the work — accurate enough to reveal irregularities in the Earth's own rotation.
- 02
Why vacuum
Air resistance and changing barometric pressure both change the rate.
- 03
Measuring the Earth
When the clock beat the planet, the planet turned out to be the unreliable one.
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