Revolutionary way of measuring wind speed

When I was very young, the road from Waterville to Cahirciveen was still unmetalled

When I was very young, the road from Waterville to Cahirciveen was still unmetalled. It was, by Kerry standards, not a winding road, and had two long stretches cutting straight across the bog. By the side of one of these was a house that was always known as tig a' doicheall.

The epithet was earned by the way the house was built. Rather than having a door which faced the road, the house presented a blank wall to the passing traveller, the entrance being located round the "back". It was said that this was done deliberately, to discourage farmers driving their cattle to the fair at Cahirciveen from entering, and availing of the warmth and shelter of the kitchen as a place to light their pipes. Hence it was tig a' doicheall, "the house that has no welcome".

In retrospect, of course, it is obvious that this sensible architectural arrangement protected the entrance from the prevailing winds that swept across the bog of Aghatubrid.

Further on the road, however, is another edifice that had a local sobriquet. Tig na gCupa, "the house of cups", was a large imposing building that got its name from a strange revolving contraption on its roof. The cups where those of a Robinson Beckley anemometer, and the tig was more properly known as Valentia Observatory, Cahirciveen.

READ MORE

It was in 1846 that Thomas Romney Robinson, then director of Armagh Observatory, hit upon the idea of using a horizontally mounted cross with "cups", whirling in the breeze, to measure wind speed. His device worked on the principle that wind exerts more pressure on the concave side of an open hemisphere than it does upon the convex surface.

A horizontal bar, free to rotate and fitted with two such hemispheres, one at each end and facing in opposite directions, will rotate with the wind because of this pressure differential. The stronger the wind, the faster it whirls. To record the wind speed, all you have to do is attach the device to a mechanism that will count the revolutions.

To deduce a precise relationship between the speed of rotation of the cups and the velocity of the wind in miles per hour, Dr Robinson resorted to the somewhat perilous expedient of mounting the instrument upon a horse and carriage which was then driven at a constant speed between two points a known distance apart on a calm day. In this way the speed of the carriage could be estimated, and after a series of such runs, the reaction of the instrument to winds of various strengths was accurately gauged.