Galileo discovered the principles of the thermometer in 1592. The Grand
Duke of Tuscany, Ferdinand II, is given credit for perfecting it in
1610. Athanasius Kircher is given credit for the discovery of the
mercurial thermometer. This was about 1641. Ferdinand the II, in 1650 or
thereabouts, filled a glass tube with colored alcohol and hermetically
sealed it after graduating the tube. Fahrenheit is given credit for the
discovery that water freezes always at the same temperature. With these
facts he devised a scale for thermometers in 1714.