††††A thermometer is an instrument for measuring temperature. The most common thermometer is a narrow, sealed tube containing a column of mercury or coloured alcohol and marked with a temperature scale. As the temperature rises, this liquid expands and the level of the column rises. As the temperature falls, the liquid contracts and the level of the column falls.
The first rather crude thermometer was made by the Italian Galileo Galilei in 1592. He used a tube of air dipped in a container of coloured liquid to indicate the temperature of the atmosphere. As the air warmed, it pushed the liquid level down. As the air cooled, the liquid level would rise again.
