Why are there 3 wet bulb thermometers in a Stevenson screen? How are they related to the Six's thermometer?

Question

Why are there 3 wet bulb thermometers in a Stevenson screen? How are they related to the Six's thermometer?

Answer 1

In a standard Stevenson screen there are four thermometers, a mercury dry bulb, mercury wet bulb, mercury maximum and alcohol minimum.

At extreme cold temperatures only the alcohol thermometer is left in the screen since mercury freezes around -39C.

The Six's thermometer is an alcohol thermometer with two stems that can record maximum and minimum temperatures but is not very accurate so is not used by people who need accurate data.

Answer 2

These three thermometers are there for the purpose of obtaining maximum, average (possibly), and minimum temperatures. Some Stevenson screens are larger than others, so there may not necessarily be three thermometers. As for Six's thermometer, its the same idea, only except it only has two thermometers that measure maximum and minimum temperatures.