Our ancestors had a sneaking suspicion that the moon was in some way responsible for many of the vagaries of weather. A crescent moon on its back, for example - when it was described as "holding water" - foretold strong but mild south-westerly gales; an upright, or "standing", crescent moon brought on the cold. And it was also believed that each lunar month took its meteorological character from the weather on the fourth and fifth days after the new moon:
The first and second never mind, The third regard not much;
But as the fourth and fifth you find,
The rest will be as such.
By the 18th century it was possible to be more precise. By dint of careful study, William Herschel, the astronomer, came to the conclusion that the character of the weather for the following seven days depended on the exact time that each of the four phases of the moon began - the New Moon, the First Quarter, the Full Moon and the Last Quarter. Thus, in winter, according to his theory, if the phase in question began between noon and 2 p.m., snow and rain would be frequent in the following week; a change of phase occurring between 2 p.m. and 4 p.m., on the other hand, indicated fair and mild weather. In this way Herschel carefully identified the significance of a lunar phase-change in each of the 12 two-hourly intervals of the day, and provided a similar tabulation for the summer months.
The fin de siecle was a popular time for lunar notions. A German meteorologist called Falb, for example, became widely known around that time as the "lunar prophet" for his alleged skill at forecasting the weather according to the motions of the moon. His methodology consisted in analysing the tidal effect of the moon upon the Earth's atmosphere, and his forecasts received great attention and were widely respected in his native country.
Meanwhile, keen weather observers in the London area thought they had firm evidence of a lunar dimension when it happened that in each of the 12 consecutive years from 1889 to 1900, a great deal more rain fell on the third, fourth and fifth days after a full moon than during the three days centred around the new moon.
Unfortunately, the relationship died away completely from 1901 onwards, and the innocent orb was restored to its former impotence. Nowadays, meteorologists react to theories such as these in much the same way as the Emperor Constantine is said to dismissed the Arian heresy: it was, he said, "a consequence of the misuse of leisure".