Weather forecasts can be a real plain

A WELL KNOWN 18th century rhyme of some considerable length lists the many signs of imminent rain

A WELL KNOWN 18th century rhyme of some considerable length lists the many signs of imminent rain. Variously ascribed to either Edward Jenner, the discoverer of smallpox vaccine, or to Erasmus Darwin, grand father of the famous Charles and a noted scientist in his own right, it runs in part:

Hark how the chairs and tables crack

Old Bette's joints are on the rack.

Now, the notion that a rise in humidity associated with the approach of rain increases the level of discomfort felt by sufferers from arthritis, is as old as humanity itself. But when the matter came to be investigated scientifically, it was found to be more complex. Dampness in the air alone, it seems, is generally not sufficient to produce the symptoms: it is also necessary for barometric pressure to be falling.

READ MORE

The series of experiments most often quoted in this context were carried out by a Dr Joseph Hollander of Pennsylvania. He used a "controlled climate chamber", constructed so it could comfortably house two patients for periods of about four weeks.

The patients chosen for observation were carefully selected as "weather sensitive" people who claimed changes in the weather worsened or improved their symptoms.

Temperature, pressure and humidity within the chamber could be carefully controlled. For part of the duration, atmospheric conditions in the chamber were kept constant; at other times pressure alone was varied by perhaps 20 millibars in a 24 hour period; at other times humidity alone was allowed to change; and sometimes both were changed together - mimicking the conditions typical of an approaching warm front.

Meanwhile, each patient noted the severity and duration of any pains, and regular objective checks were carried out on the tenderness of swelling or susceptible joints.

By and large, variations of pressure alone, or humidity alone, induced no symptoms, but when there was a simultaneous fall in pressure and a rise in the humidity, patients experienced an increase in pain - pain which was alleviated when conditions settled down again. Moreover, a succession of such changes, corresponding to what might be called a "stormy" interlude in realy life, appeared to have a cumulative effect.

The conclusion is that Old Betty's joints are a reliable indicator of the weather after all. But why this should be so in such a complex way, no one really knows.