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When Britain’s railways needed a shared clock

A timetable becomes awkward when the clocks at its two ends disagree. In nineteenth-century Britain, railway journeys helped turn local time into a shared coordination problem, while the telegraph helped distribute an answer.

5–7 min

Questions you could explore

  • Why did a railway need agreement about time?
  • How could stations receive a common time signal?

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History

Calibrating the radiocarbon clock

Carbon-14 decays at a steady, predictable rate, which makes it look like a simple stopwatch for dating ancient wood, bone, or charcoal. However, the amount of radiocarbon in Earth's atmosphere has varied over the millennia, so an accurate date relies on calibrating the measurement against tree rings and other materials whose calendar age is already known.

4–5 min

Calibrating the radiocarbon clock

History4–5 minCarbon-14 decays at a steady, predictable rate, which makes it look like a simple stopwatch for dating ancient wood, bone, or charcoal. However, the amount of radiocarbon in Earth's atmosphere has varied over the millennia, so an accurate date relies on calibrating the measurement against tree rings and other materials whose calendar age is already known.

History

How do archaeologists work out what happened first?

A deep object is not necessarily the oldest thing at an archaeological site. A later pit can cut through earlier ground, leaving a sequence that has to be reconstructed from relationships between layers.

4–6 min

How do archaeologists work out what happened first?

History4–6 minA deep object is not necessarily the oldest thing at an archaeological site. A later pit can cut through earlier ground, leaving a sequence that has to be reconstructed from relationships between layers.

History

How did reusable type change the making of a page?

In Gutenberg's Mainz workshop in the 1450s, separate pieces of metal type could form a page and be used again. Printing repeated text, but hand finishing still helped make individual Bibles differ.

5–7 min

How did reusable type change the making of a page?

History5–7 minIn Gutenberg's Mainz workshop in the 1450s, separate pieces of metal type could form a page and be used again. Printing repeated text, but hand finishing still helped make individual Bibles differ.

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