I assert that when the globe is placed in the sun and becomes warm, some of the air enclosed in the tube will pass out … into the water, setting it in motion and producing air bubbles, one after the other. If the globe be placed in the shade … then the water will rise through the tube and flow into the globe.
Some seventeen or so centuries later Philo’s idea was revisited, leading to the invention of the air thermoscope. The Italian physician Santorio Santorio was one of several Europeans working on it simultaneously.
Santorio’s instrument is in two parts. The glass bulb and tube are heated to expel some air, and the end of the tube is inverted into the narrow vessel containing water. As the air inside the bulb cools it contracts, drawing liquid up into the tube. Once it has been set up, the changing water level indicates rising and falling temperature.
Santorio later put a scale on the thermoscope, creating the first air thermometer. The air thermometer was supplanted by the more familiar liquid-in-glass thermometer from the 1640s. More on that another time.