SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Galileo thermometer. This is a glass tube filled with water containing glass bulbs of varying density. A heater is used to warm the water. As the temperature of the water increases its density decreases. At any given temperature, some of the bulbs will float and others will sink, depending on their density relative to that of the water. Here the water has been warmed sufficiently for all the bulbs to sink.
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