Mercury-in-glas thermometer, French, c 1790.
© Science Museum / Science & Society Picture Library
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.