How does galileo's thermometer work?
Answers:
See http://en.wikipedia.org/wiki/galileo_the.
http://www.howstuffworks.com/question663.
You have a bunch of glass balls, filled with some liquid, floating in some other liquid. The liquid in the glass balls has a density very close to the surrounding liquid, but that density is dependant on the temperature. So each ball has a temperature above which, the density of the liquid in the ball become less than that of the surrounding liquid, and and the ball rises. So you have a collection of glass balls, and they are each made to float at a different temeprature. So you look at the floating balls, and the one with the highest tempearture tells you the temperature of the air.
The Galileo thermometer works due to the principle of buoyancy. Buoyancy determines whether objects float or sink in a liquid, and is responsible for the fact that even boats made of steel can float (of course, a solid bar of steel by itself will sink).
The only factor that determines whether a large object will float or sink in a particular liquid relates the object's mass to the mass of the liquid displaced by the object when submerged[1]. If the object's mass is greater than the mass of liquid displaced, the object will sink. If the object's mass is less than the mass of liquid displaced, the object will float.
A Galileo thermometer, Galilean thermometer or thermoscope is a thermometer made of a sealed glass cylinder containing a clear liquid. Suspended in the liquid are a number of weights. Commonly those weights are themselves sealed glass containers with coloured liquid for an attractive effect. As the liquid changes temperature it changes density and the suspended weights rise and fall to stay at the position where their density is equal to that of the surrounding liquid. If the weights differ by a very small amount and are ordered such that the least dense is at the top and most dense at the bottom, they can form a temperature scale.
The temperature is typically read from an engraved metal disc on each weight. The lowest weight of the top set of weights indicates the ambient temperature. To achieve this requires manufacturing the weights to a tolerance of less than 1/1000 of a gram.
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