Galileo (1564-1642) first discovered that the density of a fluid is linked to temperature.  Through a series of experiments, Galileo learned that a fluid’s density increases as temperature drops, but decreases as it warms up. To demonstrate his theory, Galileo placed several liquid-filled glass spheres into a water tank to observe their reaction to temperature changes.  As he predicted, a solid body of known weight will rise or fall with fluctuations in temperature.

Each of the eleven temperature balls within this thermometer are exactly weighed and fitted with a metal Fahrenheit temperature medallion.  The thermometer measures from 62° to 82° F in steps of 2°.

Simply look at the lowest floating temperature ball within the group of balls floating at the top of the thermometer to tell the correct temperature—68° in this measurement to the left.

You will find that the balls will slowly fall as the temperature rises, and rise up again when the temperature cools.