Have you noticed it a little cool of late - cooler anyway than one might think it ought to be in August? Perhaps, as well, you hear a ghostly Scottish chuckle of "I told ye so"? That will be the ghost of Alexander Buchan, who believed that certain periods of the year are colder than they ought to be, and that other spells are warm. And one of Buchan's cold spells, from August 6th to 11th, would have ended yesterday.
Buchan was no eccentric amateur when it came to meteorology. He was one of the foremost practitioners of his day, and for more than 40 years the secretary and presiding genius of the Scottish Meteorological Society. In 1868, for example, only 10 years after Buys Ballot had enunciated his famous law about the direction in which the wind blows around a depression, Buchan refined the theory:
"The wind blows neither in a circle round the centre of a depression, nor directly towards the centre, but in a direction between the two. In effect, the direction of the wind at any place makes an angle of 60 to 80 degrees with the line which would be drawn from the place to the centre of the depression." This agrees well with today's accepted theory.
The assertions about warm and cold spells made by Alexander Buchan were firmly based on a statistical study of Scottish weather records carried out from 1857 to 1866, and were published in 1867 in a famous paper called Interruptions in the Regular Rise and Fall of Temperature in the Course of the Year.
The cold spells he identified were February 7th to 14th; April 11th to 14th; May 9th to 14th; June 29th to July 4th; August 6th to 11th; and November 6th to 13th.
The warm ones were July 12th to 15th; August 12th to 15th; and December 3rd to 14th. August, unusually, contains two Buchan spells, and those who may feel that he was right about the recent chilly weather can take succour from the fact that a warm period, from the 12th to 15th, should be due to start today.
"Buchan spells" achieved significant notoriety in the half century or so after their alleged discovery, but meteorologists now treat them with some scepticism. More sophisticated analysis over longer periods does not support their regular existence. Indeed, in fairness to Buchan, he himself never claimed his spells were an infallible guide to the weather, and only suggested that they seemed to apply in his native part of Scotland. Even so, Buchan spells, like horoscopes and old wives' tales, are fun to remember, and at least they earned one studious Scot a place in history.