A chill in the clammy air

"LET rash, gloomy and ungrateful mortals forbear to murmur against this climate," said Dr John Rutty, an 18th-century Dublin …

"LET rash, gloomy and ungrateful mortals forbear to murmur against this climate," said Dr John Rutty, an 18th-century Dublin doctor who made several detailed studies of our weather.

"It is evident that the bounty of providence causeth the sun to shine on us in a far greater degree than we commonly imagine or deserve."

Now it is difficult to agree wholeheartedly with Dr Rutty on these cheerless dark November mornings.

What affects most of us particularly, however, is not so much the modest temperature per se, but the penetrating dampness that pervades the chilling air and which is blamed for all the coughs and colds and bouts of rheumatism to which we imagine our nation to be unusually prone.

READ MORE

We compare our lot unfavourably with the nice "dry cold" of Canada, for example and other places like it. If one wanted to differentiate in numbers between "damp" cold and "dry" cold, one might define the former as corresponding broadly to a temperature regime between say, minus 3 and plus 8 combined with frequent mist rain, sleet or snow and hence a generally cloudy sky.

A dry coldness on the other hand might imply air temperatures less than minus 3 so that the air, even when saturated, contains very little moisture in absolute terms.

Most people would probably maintain that the dry cold is the more bearable of the two, but it is difficult to find physiological reasons why this should be so.

It is true that in a humid atmosphere, clothing becomes wet and therefore less effective as an insulator and that this may lead to heat loss and discomfort. Moreover, the pervasive winter dampness in an inadequately heated building is unpleasant.

Nevertheless, for a person clothed to suit the circumstances, humid cold of itself is not more penetrating or enervating than dry cold, and in terms of the physics of heat transfer, the difference between the two is negligible.

The argument that damp air conducts heat more rapidly from the body than dry air can be countered by the observation that dry air promotes more active cooling by evaporation.

It is probable that our preferences have little to do with temperature or humidity at all. Dry cold of the kind imagined and perhaps remembered is often accompanied by sunny skies add this type of weather is not only psychologically more pleasing than overcast conditions, but the absorption of solar radiation adds to one's sense of comfort.

You may feel less unhappy in "dry cold" rather than "humid cold" - but it is probably not because of the difference in humidity.