Based on a thermoscope created by Galileo Galilei in very early 1600s, this thermometer was not invented by him, but rather called a Galileo thermometer by the group of academics that invented it. The thermometer is a straightforward, fairly reliable thermometer, but today is seen more as a talking point and is mainly used for decoration and general observations. The unit consists of an enclosed glass tube that is filled with an alcohol based liquid with a small expansion air gap. The glass balloons or spheres are filled with a coloured fluid combination. This liquid mixture might have alcohol, or merely be water with food colouring.
As the temperature changes this causes the spheres to rise and fall inside the tube. Of the spheres that appear at the top half we take the lowest hanging one to be the relevant temperature. The spheres are marked 2 degrees apart, if one sphere is half way between the top and the bottom this would indicate the temperature being in the middle so if the one above is 22 the one floating mid way would be 20 meaning the temperature is around 21.
Affixed to each sphere is a little metal tag that has a temperature level on it in increments of 2 degrees. These tags are actually adjusted counterweights. So the weight of each tag is slightly different from the others. Since the spheres are blown from glass, they aren't exactly the same size and shape. The spheres are calibrated to make sure that they have a precise weight to them.
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