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 in density 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. Download high resolution version (444x1083, 298 KB)Galileo Thermometer File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (444x1083, 298 KB)Galileo Thermometer File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... KDFSAJFKASJDKFJASDKLJFDKLASJFLKJASKLFJLAKSJFLKSJALFKJSKLJFto the Sun-centered solar system which Galileo supported. ... It has been suggested that List of temperature sensors be merged into this article or section. ... Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ... A right circular cylinder An elliptic cylinder In mathematics, a cylinder is a quadric surface, with the following equation in Cartesian coordinates: This equation is for an elliptic cylinder, a generalization of the ordinary, circular cylinder (a = b). ... A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ... Glass can be made transparent and flat, or into other shapes and colors as shown in this sphere from the Verrerie of Brehat in Brittany. ... Fig. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... Fig. ...

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 (1 milligram). BIC pen cap, about 1 gram. ...

How it works

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. Image File history File linksMetadata Download high-resolution version (1536x2048, 981 KB) Galileo Thermometer detail File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Thermometer Galileo thermometer Metadata This file contains additional information, probably added from the digital camera... Image File history File linksMetadata Download high-resolution version (1536x2048, 981 KB) Galileo Thermometer detail File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Thermometer Galileo thermometer Metadata This file contains additional information, probably added from the digital camera... In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i. ... The steel cable of a colliery winding tower. ... Unsolved problems in physics: What causes anything to have mass? The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to. ...

Suppose there are two objects, each a cube 10 cm by 10 cm by 10 cm (i.e., 1 liter). The mass of water displaced by an object of this size is 1 kg. The brown object on the left is floating because the mass of water it is displacing (0.5 kg) is equal to the mass of the object. The green object on the right has sunk because the mass of water it is displacing (1 kg) is less than the object's mass (2 kg). Figure for Galileo thermometer This image has been released into the public domain by its creator and original copyright holder. ...

Not all objects made of the green material above will sink. In Figure 2, the interior of the green object has been hollowed out. The total mass of the object is now 0.5 kg, yet its volume remains the same, so it floats half way out of the water like the brown object in Figure 1. Figure for Galileo thermometer This image has been released into the public domain by its creator and original copyright holder. ...

In the examples above, the liquid in which the objects have been floating is assumed to be water. Water has a density of 1 kg/L, which means that the volume of water displaced by any of the above objects when fully submerged, is 1 kg.

Galileo discovered that the density of a liquid varies slightly with temperature. As the temperature increases, the density of the liquid decreases. This is the key to how the Galileo thermometer works.

Figure 3 shows a 1 kg hollow object made of the green material. In the left hand container, the density of the liquid is 1.001 kg/L. Since the object weighs less than the mass of water it displaces, it floats. In the right hand container, the density of the liquid is 0.999 kg/L. Since the object weighs more than the mass of water it displaces, it sinks. This shows that very small changes in the density of the liquid can easily cause an almost-floating object to sink. Figure for Galileo thermometer This image has been released into the public domain by its creator and original copyright holder. ...

In the Galileo thermometer, the small glass bulbs are partly filled with a different (coloured) liquid. Each is filled with a slightly different amount, ranging from lightest at the uppermost bulb to heaviest at the lowermost bulb. The clear liquid in which the bulbs are submerged is not water, but some inert hydrocarbon (probably chosen because its density varies with temperature more than water does). Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ...

Figure 4 shows a schematic representation of a Galileo thermometer at two different temperatures (the temperature markings on this example are in Fahrenheit). Figure for Galileo thermometer This image has been released into the public domain by its creator and original copyright holder. ... Fahrenheit is a temperature scale named after the German physicist Daniel Gabriel Fahrenheit (1686–1736), who proposed it in 1724. ...

How to read temperature with a Galilean Thermometer:

If there are some bulbs at the top (Figure 4, left) and some at the bottom, but one floating in the middle, then the one floating in the middle tells the temperature.

If there is not a bulb in the middle (Figure 4, right) then you take the temperature at the bulb at the bottom of the gap, add it to the temperature at the bulb at the top of the gap, and divide the result by two.

Selecting

When selecting a Galilean Thermometer which is intended for measuring temperature (not just looking good), check that the cylinder is sized such that the bulbs either can fit past each other so that they touch bulb to bulb, or that the disc on the upper bulb sits on the top of the lower bulb. If the disc presses on the side of the lower bulb it will increase the friction between the bulbs and the bulbs will be less likely to move up and down.

References

1. ^ Small objects, such as a pin (device), can float through surface tension.

A pin is a device used for fastening objects or material together. ... In physics, surface tension is an effect within the surface layer of a liquid that causes that layer to behave as an elastic sheet. ...

External links

• How to read a Galilean Thermometer
• Galilean Thermometer
• Howstuffworks