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How did John Snow investigate whether drinking water spread cholera?

A map of deaths raises a question; it does not answer every part of it. Snow also investigated people near the Broad Street pump who used different water supplies, including a workhouse and a brewery. Their circumstances helped him examine an explanation that proximity alone could not settle.

3–7 min

Questions you could explore

  • Why are nearby people who did not use the pump especially informative?
  • What alternative explanation would the comparisons need to address?

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History

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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.

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4–6 min

How do archaeologists work out what happened first?

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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

When Britain’s railways needed a shared clock

History5–7 minA 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.

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