There was a restricted zone in every Greek and Roman temple called the adytum, into which the hoi polloi could never gain admittance. And the Jewish Temple in Jerusalem had a similar area that was out of bounds: the holy of holies could only be entered by the high priest himself, and even in his case only once a year at Yom Kippur. But meteorologists, too, have a place like this at every major weather station. It is called the instruments enclosure.
This is a plot of ground some 30 m square, equipped to monitor the progress of the elements. It must be on level ground, well drained, and well away from any obstacles, like trees or buildings, that might interfere with the readings of the instruments.
As its name implies, it is bounded by a 6 ft fence, intended, as The Observer's Handbook very clearly says, "to exclude unauthorised admittance". The whole area is set in grass, meticulously trimmed, and has narrow paths leading from one to another of the instruments.
At one corner is the Stevenson screen, a white louvred cabinet which houses the thermometers and protects them from direct exposure to the wind and sun. The ground thermometers are carefully deployed on the short grass nearby, while others are submerged at various depths to measure the temperature at standard distances beneath the surface of the soil.
Near the centre of the enclosure is what, in the jargon used by meteorologists, is called a Class A Pan, a shallow 4 ft dish of water used to monitor evaporation. And not too far away, gauges capture the falling rain to provide statistics for posterity.
In another part of this weather reservation, enshrined on a 6 ft pedestal, sits the sunshine recorder with its sphere of glass acting as a simple lens to burn a trace on the graduated card beneath.
At other sites are cabinets to collect rainwater for pollution or radioactivity analysis, or to house pumps to filter the air for similar examination. And pride of place in the enclosure goes to a 6 ft square patch of bare soil, used to monitor the "state of ground"; whether it be wet or waterlogged, or dry, or covered to a certain depth by snow, or white with frost.
It is to this hallowed site that the observer makes an hourly pilgrimage. He or she follows an almost ceremonial routine around the instruments to note their readings. Then, with the gate of the enclosure gently closed to debar the unelect, the instruments are left for 60 minutes undisturbed to keep their vigil.