John Earle suggests that the legend comes from a pagan or possibly prehistoric day of augury. In France, St. Medard (8 June), Urban of Langres, and St. Gervase and St. Protais (19 June) are credited with an influence on the weather almost identical with that attributed to St Swithun in England. In Flanders, there is St Godelieve (6 July) and in Germany the Seven Sleepers' Day (27 June). There is a scientific basis to the weather pattern behind the legend of St Swithun's day. Around the middle of July, the jet stream settles into a pattern which, in the majority of years, holds reasonably steady until the end of August. When the jet stream lies north of the British Isles then continental high pressure is able to move in; when it lies across or south of the British Isles, Arctic air and Atlantic weather systems predominate.