Tyndall's boiling point apparatus, 1880.
© Science Museum / Science & Society Picture Library
John Tyndall (1820-1893), an Irish physicist, was interested in how heat causes changes of state. This apparatus demonstrates that water which is not hot enough to boil at ordinary atmospheric presure will begin to boil when the presure on it is reduced. This is why water boils at a progresively lower temperature at increasing altitudes. Apparatus made by J J Griffin and Sons, London.