Galileo's Early Thermometer Prototype

Timeline

1. c. 1592–1595Padua · VenetoGalileo built an open gas thermoscope from a glass bulb, narrow tube, and water vessel, using heated air expansion to move a liquid column, allowing qualitative comparison of temperature changes across places and times, though without a unified scale.
2. c. 1603–1610Venice · VenetoGalileo and Venetian scholars such as Sagredo continued refining the thermoscope; Castelli saw the device firsthand around 1603, providing direct witness for his later accounts and dissemination.
3. c. 1612–1625Padua · VenetoSantorio Santorio added numerical scales to Galileo's thermoscope, creating a thermometer that could quantify body and room temperature, and conducted systematic meteorological and medical temperature observations, marking the entry of heat measurement into a quantitative phase.