Good Questions: Going down the plughole

IS IT true that in the southern hemisphere, bath water runs out in the opposite direction from ours in the UK? If it is, where does it change direction, and what happens there? (William Watts, London SW16).

In a world with perfect plumbing, bath water would disappear anti-clockwise in the northern hemisphere, clockwise in the southern hemisphere, and vortex-free straight down the equatorial plughole. This is due to the Coriolis force, which is an effect of the earth's rotation.

As the earth rotates from west to east, points on its surface have varying velocities, fastest at the equator, slowest at the poles. A projectile aimed due north from the equator will begin its journey with a faster eastward speed than the point it is aimed at. It will therefore drift east of its target. Similarly, anything aimed southwards towards the equator will have drifted west by the time it arrives.

Applying this to the British plughole, the water north of the plug drifts towards the western edge of the hole, while the water on the other side of the plug heads for the eastern side. The overall effect is to produce an anti-clockwise vortex. In Australia, a clockwise vortex results.

The Coriolis effect on bath water, however, is so small that it will be drowned by any currents already existing in the water, or caused when the plug is pulled, or by irregularity in the bath's architecture, or the water's temperature, or the alignment of the plughole.

In the 1970s, Nature reported some experiments conducted with a perfectly circular bath, with its plughole and taps centrally located, the plug removed from below, the water allowed to stand for several hours to eliminate currents and temperature differentials, and the whole apparatus covered to avoid the effects of air movement.

While experiments in New York and Melbourne tended to support the theory outlined above, there were still grounds for believing that further research is needed. For one thing, they used different baths in the two cities, so it could all have been due to the plumbing.

Why, in reports of legal processes, do we frequently read of a subpoena being served, and never of the full poena? (C W Morton, London N4).

The poena is what you get if you don't do what the subpoena tells you. The first two Latin words on a subpoena are sub poena - 'under penalty'.

Did Humpty Dumpty fall, was he pushed or had he been drinking? And how could anyone expect a horse - even one of the king's - to put a broken egg together again? (Charles Crawford, Shrewsbury)

Most sources suggests the poem is an ancient riddle, to which the answer is 'egg'. Similar poems exist in other European cultures with the egg named Hillerin-Lillerin (Finland), Lille-Trille (Demmark), Humpelken-Pumpelken (parts of Germany), Annebadadeli (Switzerland), Thille Lille (Sweden), and Trille Trolle, Etje-Papetje, Wirgele-Wargele, Gige-le-Gagele or Runtzelten-Puntzelten (other parts of Germany).

Humpty Dumpty is also the name of a 19th-century American game, in which girls would hold their skirts tightly round their feet while seated, then fall over backwards and try to regain their balance.

Lina Eckerstein, in her Comparative Studies in Nursery Rhymes (1906) makes the valid point that sitting on a wall is, for an actual egg, an impossible situation. She believes the rhyme may be taken to describe people personating eggs.

In this context, she also mentions the Finnish epic, the Kalevala, in which an egg represents the origin of life. 'The world-egg broke. Its upper part became the vault of heaven, its lower part the earth. The yolk formed the sun, the white the moon, and the fragments of the shell became the stars in heaven.'

So the failure of the king's horses and men could symbolise man's insignificance compared with cosmic forces. On the other hand, humpty-dumpty was the name for a boiled ale and brandy drink in the 17th century, so intoxication cannot be ruled out.

Sources: Oxford Companion to Children's Literature, Oxford Dictionary of Nursery Rhymes.

(Photograph omitted)