Galileo Galilei was born at Pisa, in Italy, in 1564. He was a professor of mathematics. He had a large number of discoveries to his credit. One of his discoveries is thermometer.
Evidence exists of a thermometer that was made as long ago as 200 B.C. Galileo made a thermometer in A.D. 1592 which was similar to the earlier one. The thermometer had no standard scale. This was an air thermometer, which worked on the principle that the higher the temperature the lower is the level of water in the stem. The bulb containing air was used to take a temperature. Heat caused the air to expand in the flask and push the water further down in the glass tube.