400
although he did most likely make the first thermometer it was not the one we use today. Daniel Gabriel Fahrenheit was the one to put the mercury into the thermometer to make them more accurate. when the mercury in the glass tube heat up it expands going up showing showing the temperature by the lines marked. yet as if this was not enough he invented the temperature scale that is still used today in the united states, Fahrenheit.
did Galileo invent the thermometer we know today?