How does a Galileo thermometer work?

How does a Galileo thermometer work?

One of my co-workers has an interesting thermometer on his desk. It is a glass tube with different-colored floating things in it. What kind of thermometer is this, and how does it work?

Glass Galileo Thermometer With Gift Box Room Temperature 18 26

Galileo Thermometer – The Science Museum of Minnesota

HOW DOES A GALILEO THERMOMETER WORK, AND HOW TO READ IT

13 Tall Galileo Thermometer With Wooden Base

Glassic Gifts® Galileo Thermometer (13 Tall

Simple Ways to Read a Galileo Thermometer: 8 Steps (with Pictures)

Cylindrical thermometer and barometer set; inspired by Galileo's instruments Interprets temp and weather based on principles of buoyancy and air

AcuRite 00795A2 Galileo Thermometer with Glass Globe Barometer, Barometer Set, Glass/Wood, 3

The Galileo Thermometer 11 — Heebie Jeebies USA

SP Bel-Art SP Bel-Art, H-B DURAC Galileo Thermometer; 18 to 26C

HOW DOES A GALILEO THERMOMETER WORK, AND HOW TO READ IT