Italian scientist Galileo made the world's first thermometer.

Answer: The glass bulb of this thermometer is air. When measuring the temperature of an object, the glass bulb should be in contact with the object. The higher the temperature, the larger the air volume in the tube and the more the liquid column drops.

Therefore, when using this thermometer, the glass bulb of the thermometer is in full contact with the object to observe the change of the liquid column. The lower the liquid column, the higher the temperature of the measured object.