Guericke's air thermometer, 1672.
© Science Museum / Science & Society Picture Library
Plate from Otto von Guericke's 'Experimenta Nova Magdeburgica'. This thermometer was over twenty feet in length and this plate shows how it would have been fixed to a wall of a house. The instrument on the left consists of a large copper sphere to which is attached one arm of a long U-tube containing alcohol. The other arm, on the right, is open to the air, and within it hangs a float counterbalanced by a figure of an angel which serves as an indicator on a scale of seven degrees, from 'great heat' to 'great cold'.