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A maximum–minimum thermometer. The scales are
Fahrenheit on the inside of the U and Celsius on the outside. The current temperature is 23 degrees Celsius, the maximum recorded is 25, and the minimum is 15; both read from the base of the small markers in each arm of the U tube. The bulbs are hidden by
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Before a new maximum or minimum reading can be taken, the thermometer must be reset by moving the markers to the top of the mercury, usually by hand using a small magnet to slide them along the tube. Any change in temperature after that will push one of the markers along with it. (If the markers are
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Detail of the thermometer bulbs of the maximum-minimum thermometer shown above. The left-hand (minimum arm) bulb is full of alcohol. This bulb measures the temperature by the expansion and contraction of the liquid. The right-hand (maximum arm) bulb contains alcohol and a bubble of low-pressure gas
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In a variation of design, some models have unsprung markers held in place by a magnetic plate located behind the card showing the scales and close enough to the U-shaped tube to hold the markers in place unless they are pushed by the thermal expansion of the device. When manual control is operated,
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and contraction of the alcohol in the first bulb as it responds to the external temperature. The vacuum in the other bulb allows free movement of the alcohol and mercury. It is the alcohol that measures the temperature; the mercury indicates the temperature reading on both scales. This is unlike a
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The thermometer shows a reading at the top of the mercury section on both the maximum and minimum scales; this shows the current temperature and should be the same on both scales. If the two readings are not the same, then the instrument scales are not correctly positioned or the instrument is
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If the temperature rises, the maximum scale marker will be pushed. If it falls, the moving mercury will push the minimum scale marker. As the temperature varies, the markers will remain in their positions unless the temperature becomes higher (for maximum) or lower (for minimum) than already
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recorded, in which case the relevant marker is pushed further. The markers thus record the furthest point reached by the mercury in each arm of the tube, and thereby the highest and lowest temperatures since the last reset. Typically the thermometer is reset every 24 hours to measure the
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The maximum and minimum readings are recorded by two small steel markers which are sprung into the capillary tube so that they can slide, but only if a force is applied to them, either by being pushed by the mercury or under the influence of an external
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Another design has the U orientated horizontally and the markers completely free and unsprung. The reset is carried out by turning the U to the vertical so the markers sink to rest on the mercury, and returning it to the horizontal.
157:, the positions of the ends of the markers nearest to the mercury are examined. Their positions on the maximum and minimum scales show the highest and lowest temperatures encountered since the last reset.
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In 2006, S.Brannan & Sons Ltd, a UK company, was granted a patent for a mercury-free version of Six's maximum-minimum thermometer: instead of alcohol and mercury two other
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or alcohol vapor. This bulb accommodates the expansion in the other bulb and allows the train of alcohol and mercury to move in the U-shaped tube as the temperature changes.
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liquids are used as the expansion and transfer liquids in the same fashion as the mercury version to position magnetic markers. In the patent,
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Marker showing the maximum temperature. Mercury has retreated to about 26.5°C as the temperature has dropped below its maximum of about 28.3°C.
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reached over a period of time, for example 24 hours. It is used to record the extremes of temperature at a location, for instance in
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the plate is pushed away from the U-shaped tube, freeing the markers which then drop under gravity to the surface of the mercury.
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Austin and McConnell, Notes and
Records of the Royal Society of London * Volume. 35, No. 1, July., 1980 at JSTOR
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The thermometer indicates the current temperature, and the highest and lowest temperatures since the last reset.
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294:, Staffordshire School Weather Data Site, Alan Rodgers & Angella Streluk, 7 March 2010, Accessed April 2011
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not reset, they will register maxima and minima only if they exceed the values already encountered.)
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with two separate temperature scales set along each arm of the U. One of these is for recording the
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Article on Six's thermometer at the Museum of the
History of Science at Florence, Italy
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O Level
Physics Notes, A Star Maths and Physics. 24 December 2010, Accessed April 2011
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maximum–minimum, minimum–maximum, maxima–minima or minima–maxima thermometer
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Hamilton, John
Montgomery; Perkins, Peter Graham (14 March 2006).
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Six's
Maximum and Minimum thermometer consists of a U-shaped
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Two hundred years of the Six's Self
Registering Thermometer
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By John Avison, page 180, Publisher Nelson
Thornes, 1989
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A History of the
Thermometer and Its Uses in Meteorology
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by Amit Batra, Johns
Hopkins University Press, 1966;
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often include a maximum-minimum registering feature.
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391:Explanation of the working of Six's thermometer
178:The original Six's thermometer design contains
92:temperature encountered and the other for the
306:"EU bans mercury in barometers, thermometers"
182:, which has been banned for most uses in the
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58:. It was invented by the British scientist
368:by James Six, Nimbus Publishing Ltd,1980;
174:Mercury-free maximum–minimum thermometers
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239:Synonyms Monthly Meteorological Magazine
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197:was chosen as the expansion liquid and
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112:In the bend of the U is a section of
96:temperature (or low pressure alcohol
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201:was chosen as the transfer liquid.
186:and some other parts of the world.
218:Maximum minimum temperature system
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366:The Construction of a Thermometer
48:maximum and minimum temperatures
242:. H.M. Stationery Office. 1869.
69:It is also commonly known as a
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328:"Maximum/minimum thermometer"
155:diurnal temperature variation
18:Maximum minimum thermometer
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304:Jones H. (July 10, 2007).
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259:The World of Physics
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123:mercury thermometer
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312:2008-05-30
224:References
191:immiscible
86:glass tube
308:. Reuters
137:damaged.
60:James Six
404:Category
333:16 April
212:See also
195:toluene
180:mercury
121:normal
114:mercury
94:minimum
90:maximum
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143:magnet
98:vapour
62:, in
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