E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
If it rains on St. Swithins day (15th July), there will be rain for forty days. (See GERVAIS.)
St. Swithins day, gif ye do rain, for forty days it will remain;
St. Swithins day, an ye be fair, for forty days twill rain nae mair.
The French have two similar proverbsSil pleut le jour de St. Médan (8th June), il pleut quarante jours plus tard; and Sil pleut le jour de St. Gervais (19th June), il pleut quarante jours après.
The legend is that St. Swithin, Bishop of Winchester, who died 862, desired to
be buried in the church-yard of the minster, that the sweet rain of heaven might fall upon his grave. At canonisation the monks thought to honour the saint by removing his body into the choir, and fixed July 15th for the ceremony; but it rained day after day for forty days, so that the monks saw the saints were averse to their project, and wisely abandoned it.
The St. Swithin of Scotland is St. Martin of Bouillons. The rainy saint in Flanders is St. Godeliève; in Germany, the Seven Sleepers.