Mercury-in-glas thermometer, French, c 1790.

Mercury-in-glas thermometer, French, c 1790.

© Science Museum / Science & Society Picture Library

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Made by Pierre Casati, this was one of the first to use the Celsius scale of heat measurement, invented in 1742 by the Swedish astronomer, Anders Celsius (1701-1744). The Celsius, or Centigrade, scale initially placed 0 degrees as water's boiling point and 100 degrees as its freezing point. In 1743, Jean-Pierre Christin, of the Societe Royale of Lyon, reversed this, making 0 degrees freezing point and 100 degrees boiling point. This is noted on the thermometer's scale, which is graduated from -35 to +100 degrees.
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