How Six max. and min. Are used to record temperature
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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 a plastic housing.
Six's thermometer is a registering thermometer which can record the maximum and minimum temperatures 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 meteorology and horticulture. It was invented by a British scientist James Six, born in Canterbury, in 1780;[1] the same basic design remains in use.
It is also commonly known as a maximum–minimum, minimum–maximum, maxima–minima or minima–maxima thermometer, of which it is the earliest practical design.
The thermometer indicates the current temperature, and the highest and lowest temperatures since last reset.
DescriptionEdit
This describes the traditional construction. Modern designs may substitute less toxic materials but operate in the same way.
It consists of a u-shaped glass tube with two separate temperature scales set along each arm of the U. One of these is for recording the maximum temperature encountered and the other for the minimum temperature. The arms of the U-shaped tube terminate in sealed glass bulbs. The bulb at the top of the minimum reading scale arm is full of alcohol, the other contains a vacuum (or low pressure alcohol vapour).[2]

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 or alcohol vapour. 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.[3]
In the bend of the U is a section of mercury, a metal which is liquid at normal temperatures. This is pushed around the tube by the thermal expansion and contraction of the alcohol in the first bulb as it responds to the external temperature. The vacuum in other bulb allows free movement of the alcohol and mercury. It is the alcohol which measures the temperature; the mercury indicates the temperature reading on both scales. This is unlike a normal mercury thermometer, in which the expansion and contraction of mercury itself indicates temperature.[2]

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.
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 damaged.[2]
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 magnet.
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 not reset, they will register maxima and minima only if they exceed the values already encountered.)
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 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 diurnal temperature variation, 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.[4
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 a plastic housing.
Six's thermometer is a registering thermometer which can record the maximum and minimum temperatures 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 meteorology and horticulture. It was invented by a British scientist James Six, born in Canterbury, in 1780;[1] the same basic design remains in use.
It is also commonly known as a maximum–minimum, minimum–maximum, maxima–minima or minima–maxima thermometer, of which it is the earliest practical design.
The thermometer indicates the current temperature, and the highest and lowest temperatures since last reset.
DescriptionEdit
This describes the traditional construction. Modern designs may substitute less toxic materials but operate in the same way.
It consists of a u-shaped glass tube with two separate temperature scales set along each arm of the U. One of these is for recording the maximum temperature encountered and the other for the minimum temperature. The arms of the U-shaped tube terminate in sealed glass bulbs. The bulb at the top of the minimum reading scale arm is full of alcohol, the other contains a vacuum (or low pressure alcohol vapour).[2]

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 or alcohol vapour. 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.[3]
In the bend of the U is a section of mercury, a metal which is liquid at normal temperatures. This is pushed around the tube by the thermal expansion and contraction of the alcohol in the first bulb as it responds to the external temperature. The vacuum in other bulb allows free movement of the alcohol and mercury. It is the alcohol which measures the temperature; the mercury indicates the temperature reading on both scales. This is unlike a normal mercury thermometer, in which the expansion and contraction of mercury itself indicates temperature.[2]

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.
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 damaged.[2]
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 magnet.
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 not reset, they will register maxima and minima only if they exceed the values already encountered.)
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 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 diurnal temperature variation, 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.[4
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