Pixii pyrometer, mid 19th century.
3 4 c m
actual image size: 32cm x 26cm

Pixii pyrometer, mid 19th century.

© Science Museum / Science & Society Picture Library


A solid expands when it is heated, because its molecules vibrate more vigorously and need more space. This pyrometer, or 'heat-measurer', demonstrated how a metal rod increased in length as it was heated by a gas flame placed beneath it, and shrank again as it cooled.

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