Which scientist is credited with creating the first open thermometer?

Galileo Galilei is recognized for creating the first open thermometer, known as the thermoscope, in the late 16th century. This instrument utilized air displacement to indicate temperature changes. As the air temperature increased, the air in the thermoscope expanded, causing liquid (often water or another fluid) to rise in a tube, and when the temperature decreased, the liquid would fall. This principle of measuring temperature through shifts in fluid level is foundational to the development of thermometers.

Galileo's innovation marked a significant advancement in the understanding of temperature measurement, which was a critical step toward the modern thermometers we use today. The thermoscope laid the groundwork for later improvements and designs, leading to more precise and reliable temperature measurement tools.