Six's Maximum and Minimum Thermometers

You may want to know what the highest (maximum) or lowest (minimum) temperatures have been in the last 24 hours. However you will not want to have to keep reading the thermometer, especially during the night. For this you will need to use a Six's thermometer. There are many sorts. This page tells you about some of them.

The bulb of the sixes thermometer in the Stevenson Screen should be approximately 1.2m (120cm) above the ground.

To see more different thermometers you can go to More About Temperature Readings or you may want to go back to the Temperature Readings page. Alternatively you may want to return to Collecting Data.

Six's Thermometer

The thermometer on the right is a special one for recording maximum and minimum temperatures. All Six's thermometers have one long 'U' shaped tube. This can be clearly seen in the image further down the page.

There is a bulb of alcohol at the top of the tube on the left. This cannot be seen on this thermometer. The alcohol expands or contract as the temperature changes. It then push round the indicator liquid to show the temperature. This example has no mercury, and is therefore safer.

You get to see the temperature twice, it should show the same temperature on both scales. Both Celsius scales show 19 °C.

no mercury six's

The Marker Pins

So that the Maximum (hottest) and Minimum (coldest) temperatures can keep be recorded there are two small steel pins.
When the temperature rises, the marker 'pin' in the right hand column is moved. It will stay there until you reset it. You read the bottom of the 'pin'. This example is 28°C.
When the temperature falls, the marker in the left hand column will be moved to show the minimum temperature. Read the 'pin' at the bottom point. This example is 16°C. See more about reading the scales below.

Reading the Scales

The close-up of a part of the scales on the right shows how they are reversed.
The right hand scale, for the maximum temperature, is the 'normal' way up. The larger numbers are at the top. Below the zero are the minus numbers (shown here in red).
The left hand scale, for recording the minimum temperatures, is reversed. The larger numbers are at the bottom. The minus numbers are above the zero (see the plus and minus signs).
When reading the temperatures that the pins were left at, always start at the zero and look carefully whether the number should be a positive number or a negative number.

max min scale

Resetting a Six's Thermometer

There are different ways of resetting the thermometer so that the pins move back to the current temperature.This is done at 09.00 GMT in the United Kingdom. Elsewhere it is 09.00 local time. Some thermometers simply have a little magnet which is used to pull the pins back down.
The video clip on the right shows a device where a magnetic strip stops the pins from falling down when the temperature changes. When the button is turned the magnet is pushed away from the pins and gravity can pull the pins down to the current temperature. If you look closely you will see the pins going down.

On other Six's thermometers when a button is pressed a similar thing happens. See a video of resetting by pressing a button.


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[Video Transcript]

Caring for a Six's Thermometer

As with most weather instruments you need to treat a Six's thermometer very carefully. There are glass parts which can be easily broken. If any instrument gets broken seek advice from an adult immediately.
When you buy a Six's thermometer make sure that the indicator liquid does not have any gaps in it. Also check that the pins are not buried in the indicator liquid.
Although many Six's thermometers have mercury for the indicator liquid there are ones without this poisonous metal. The one on the right has mercury in it. You can see the shiny silver colour. It may be better to purchase one without mercury. Search the internet for a supplier.

Error Checking

When you record your data from your sixes thermometers you will record three numbers. These are the maximum and minimum temperatures and the current temperature. The highest number will be the maximum, the lowest the minimum, and the current temperature will be somewhere in between. Once you have recorded the number take a moment to check that they are in the right boxes. Can you see any incorrectly typed number on the right?
See these rules carefully explained in this Notes file.
See activities about maximum and minimum temperatures on the far right near the top of the page.

an example of a wrongly typed spreadsheet

James Six (1731 - 1793)

This is called a Six's thermometer because it was invented by a man called James Six.He was born in Canterbury and did some scientific experiments in the cathedral. The picture on the right shows this beautiful cathedral.
As part of his science experiments he wanted to record the weather and did not want to keep getting up in the night to take readings. For this reason he invented this sort of maximum and minimum thermometer.

canterbury cathedral

Why record Maximums and Minimums?

Most people love record breakers. If you only record the temperature when you are looking at your thermometer you might miss a record breaking temperature, either a maximum or a minimum. If you have a Sixes Thermometer, or a digital maximum and minimum thermometer you will record the highest and lowest temperature whatever time they occur.

There are some environments where it is important to know how hot or cold it is getting. In a greenhouse plants need particular conditions to grow. Monitoring the temperature will help plan caring for them. If the maximum temperature is too high some means of cooling the greenhouse down can be sorted out. If it is getting cold (perhaps in the middle of the night) a heater can be used. Monitoring conditions in many other places is also important; classrooms, hospitals, libraries, museums...

Recording this data over a period of time means that changes in the climate can be observed. Meteorologists look back into records from many years ago to see what is happening in the long term.



Please Note

Please be conscious of any safety issues regarding these activities. It may be advisable to avoid any instruments which contain mercury.