Galileo Thermometer - Wikipedia

Thermometer containing several glass vessels of varying density

A Galileo thermometer (or Galilean thermometer) is a thermometer containing a clear liquid and several glass vessels of varying density. The individual floats rise or fall in relation to their respective density and the density of the surrounding liquid as the temperature changes. It is named after Galileo Galilei because he discovered the principle on which this thermometer is based—that the density of a liquid changes in relation to its temperature.

History

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Although named after the 16th–17th-century physicist Galileo, the thermometer was not invented by him. (Galileo did invent a thermometer called Galileo's air thermometer, more accurately called a thermoscope, in or before 1603.)[1]

The instrument now known as a Galileo thermometer was invented by a group of academics and technicians known as the Accademia del Cimento of Florence,[2] who included Galileo's pupil, Torricelli and Torricelli's pupil Viviani.[3][4] Details of the thermometer were published in the Saggi di naturali esperienze fatte nell'Academia del Cimento sotto la protezione del Serenissimo Principe Leopoldo di Toscana e descritte dal segretario di essa Accademia (1666), the academy's main publication. The English translation of this work (1684) describes the device ('The Fifth Thermometer') as 'slow and lazy', a description that is reflected in an alternative Italian name for the invention, the termometro lento (slow thermometer).[5] The outer vessel was filled with 'rectified spirits of wine' (a concentrated solution of ethanol in water); the weights of the glass bubbles were adjusted by grinding a small amount of glass from the sealed end; and a small air space was left at the top of the main vessel to allow 'for the Liquor to rarefie' (i.e. expand).

The device now called the Galileo thermometer was revived in the modern era by the Natural History Museum, London, which started selling a version in the 1990s.[6]

Operation

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In the Galileo thermometer, the small glass bulbs are partly filled with different-colored liquids. The composition of these liquids is mainly water; some contain a tiny percent of alcohol, but that is not important for the functioning of the thermometer; they merely function as fixed weights, with their colors denoting given temperatures. Once the hand-blown bulbs have been sealed, their effective densities are adjusted using the metal tags hanging from beneath them. Any expansion due to the temperature change of the colored liquid and air gap inside the bulbs does not affect the operation of the thermometer, as these materials are sealed inside a glass bulb of approximately fixed size. The clear liquid in which the bulbs are submerged is not usually water, but some organic compounds (such as ethanol or kerosene) the density of which varies with temperature. The fixed size of the outer tube ensures that the outer clear liquid will be in gas-liquid equilibrium. Even so, the equilibrium density of liquids like ethanol [7] decreases with an increase in temperature and this causes the bulbs to rise or sink accordingly.[2]

As the temperature rises the bulbs will sink one by one according to their individual density as the clear holding fluid's density gradually changes around them. Eventually all the bulbs may be at the base of the tube depending on the temperature of the surroundings and therefore that of the clear holding fluid. As the temperature falls the reverse happens with the bulbs, until they can all be at the top.

The metal tags on each bulb are stamped with a temperature. If a bulb is in the centre of the column, that gives a close approximation of the environment temperature outside the tube. If there are some at the top and some at the base but none in between the average of the lowest bulb at the top and the highest at the base provides that figure.

Gallery

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• Figure 1
• Figure 2
• Figure 3

See also

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• Cartesian diver – Classic science experiment demonstrating the Archimedes' principle and the ideal gas law
• Frog thermometer – Type of clinical thermometer

References

[edit] Wikimedia Commons has media related to Galileo thermometer.

1. ^ Aleksandr Khristoforovich Khrgian, Meteorology: a historical survey, Volume 1, Israel Program for Scientific Translations, 1970, p. 25
2. ^ a b Loyson, Peter (2012). "Galilean Thermometer Not So Galilean". Journal of Chemical Education. 89 (9): 1095–1096. Bibcode:2012JChEd..89.1095L. doi:10.1021/ed200793g.
3. ^ Fretwell, Mattie Bell (February 1937). "The Development if the Thermometer". Mathematics Teacher. 30 (2): 80–83. doi:10.5951/MT.30.2.0080. JSTOR 27952013.
4. ^ A. Frova & M. Marenzana, Thus spoke Galileo, p.348, accessed on Google Books 2012-06-14, itself based on R. Caverni, Storia del metodo sperimentale in Italia, Vol. 2, Florence, 1895
5. ^ José Montesinos, Carlos Solís Santos [eds], Largo campo di filosofare: Eurosymposium Galileo 2001, Fundación Canaria Orotava, 2001
6. ^ Daily Mirror, 28 January 1994, p. 28
7. ^ "Ethanol - Density and Specific Weight vs. Temperature and Pressure".

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v t e Galileo Galilei
Scientific career	Observational astronomy Galileo affair Galileo's escapement Galilean invariance Galilean moons Galilean transformation Leaning Tower of Pisa experiment Phases of Venus Celatone Thermoscope
Works	De motu antiquiora (1589–1592) Le mecaniche (1593-1608) Sidereus Nuncius (1610) Letters on Sunspots (1613) Letter to Benedetto Castelli (1613) "Letter to the Grand Duchess Christina" (1615) "Discourse on the Tides" (1616) Discourse on Comets (1619) The Assayer (1623) Dialogue Concerning the Two Chief World Systems (1632) Two New Sciences (1638)
Family	Vincenzo Galilei (father) Michelagnolo Galilei (brother) Vincenzo Gamba (son) Maria Celeste (daughter) Marina Gamba (mistress)
Related	"And yet it moves" Villa Il Gioiello Galileo's paradox Galileo's ship Sector Museo Galileo Galileo's telescopes Galileo's objective lens Tribune of Galileo Galileo thermometer Galileo project spacecraft Galileo Galilei Airport Galileo National Telescope Astronomers Monument
In popular culture	Life of Galileo (1943 play) Lamp At Midnight (1947 play) Galileo (1968 film) Galileo (1975 film) Starry Messenger (1996 book) Galileo's Daughter: A Historical Memoir of Science, Faith, and Love (1999 book) Galileo Galilei (2002 opera) Galileo's Dream (2009 novel)