Temperature Readings

Thermometers are used to measure temperature. There are lots of different sorts of thermometers, each having a different use. This page describes just a few of them. To see more different thermometers you can go to More About Temperature Readings. There is also a whole page about Six's maximum and minimum thermometers. You might also like to complete the Temperature Reading Quiz.

It is important to measure the temperature, as this makes a big difference to us in many ways. Farmers need to know when their seed will germinate, drivers need to know if there will be ice on the roads. Can you think of other reasons why we need to know how warm or cold it is?

When you have finished reading about this you may want to return to Collecting Data. If you want cooling down you could got to Below Freezing, or if you want warming up you could go to Sunshine.

Where to Put Your Thermometers The thermometers need to take readings in the shade for good results. Other weather watchers will be taking their readings in the shade and you want your readings to be able to be compared. The best place to put your thermometers is in a Stevenson screen. If you have not got a Stevenson screen, and really cannot make one using these instructions, you need to make sure that you put your thermometers on a north facing wall or post. This will shade them as much as possible. The photograph on the right shows a weather station made from one plank of wood. It has holes to allow the air to circulate. The door opens to the north so that even when it is open the sun will not shine directly into it.
Units of Measurement All temperatures are recorded in degrees Celsius (ºC). This is the standard unit in Europe and most of the world. When reading the scale check first to see what each mark represents. On this scale, from the wet thermometer, each line represents one degree Celsius. You can then count on or back from the nearest number. This thermometer is reading just above 17ºC.
Data Checking All temperature reading numbers should be reasonable. Some high numbers should be regarded as suspicious in the winter time. Would you expect 15ºC in winter? Very low numbers should also be looked at closely in summer. Would you expect 5ºC in summer? You should ask yourself if your readings are sensible. When the temperature drops below 0ºC water will freeze. This causes various types of frost. The frost on the rain gauge in the picture on the right was very pretty.
Maximum and minimum temperature Maximum temperature is the warmest (largest number) since the last reading. The Minimum temperature is the coldest (smallest number) since the last reading. The maximum temperature should never be smaller than the minimum temperature. The thermometer on the right is a special one for recording these temperatures. This is called a Six's thermometer because it was invented by a man called James Six. See more about these useful thermometers on the Six's Thermometers page.
Dial Maximum and Minimum Thermometer This thermometer shows the temperature by a needle pointing to a number on a dial. There are also two pointers which get pushed by the black pointer. The red one shows the maximum temperature and the blue one shows the minimum temperature. These thermometers do not have mercury or spirit to react to the temperature, they have a special metal strip.	[Video transcript]
Wet and Dry Temperatures The current temperature is taken from the dry temperature reading. The purpose of the wet and dry temperatures is to allow you to work out the humidity of the air. See the Humidity page for more details.
Checking Wet and Dry Readings The wet temperature reading should not be bigger that the dry temperature. This is because when things are wet they are colder. On very dry sunny days these temperatures will be further apart. It is usual for the two temperatures to be fairly close together when it is raining.
Maintenance Make sure that the reservoir of water is topped up with clean distilled water. If it runs dry you will have two dry thermometers! The little bottle unscrews so that you can fill it.
Using ICT There are many cheap digital thermometers these days. The instrument in the image can measure the current, maximum and minimum temperatures in two locations. One reading is taken from an internal sensor, the other uses the probe on the end of the cable. See more information on the ICT page.