Heat has always been something we thought we understood. From baking bread to running engines, the idea seemed simple: heat spreads out smoothly, like water soaking through a sponge. That simple ...

So long as the mild heat or cold source is present, it will run. It was invented in 1816 by Reverend Dr. Robert Stirling, a Scottish clergyman and engineer, as an alternative to steam engines, which, ...

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