Question

Why are instruments such as thermometers kept in a Stevenson screen​

Answer 1

They protect the temperature sensors from being influenced by direct or reflected sunlight.
Stevenson screens are always installed so that the door opens facing north, to keep the sun from shining directly on the thermometers and affecting the readings.

Answer 2

So it can be kept in a environment to measure temperatures :3

Step-by-step explanation:

:3