Based on a thermoscope invented by Galileo Galilei in the early
1600s, the thermometer on your co-worker's desk is called a
Galileo thermometer. A simple, fairly accurate thermometer,
today it is mostly used as decoration. The Galileo thermometer
consists of a sealed glass tube that is filled with water and
several floating bubbles. The bubbles are glass spheres filled
with a colored liquid mixture. This liquid mixture may contain
alcohol, or it might simply be water with food coloring.
Attached to each bubble is a little metal tag that indicates a
temperature. A number and degree symbol are engraved in the tag.
These metal tags are actually calibrated counterweights. The
weight of each tag is slightly different from the others. Since
the bubbles are all hand-blown glass, they aren't exactly the
same size and shape. The bubbles are calibrated by adding a
certain amount of fluid to them so that they have the exact same
density. So, after the weighted tags are attached to the
bubbles, each differs very slightly