The passage in Clark's folio volume, 'A Survey of the Lakes', etc., which suggested to Wordsworth the above lines in the 'Evening Walk', is to be found in chapter i. of the second book, p. 55. It gives a weird account of the appearance of horsemen being exercised in troops upon "Southen-fell side, as seen on the 25th of June 1744 by William Lancaster of Blakehills, and a farm servant, David Strichet: "These visionary horsemen seemed to come from the lowest part of Southen-fell, and became visible just at a place called Knott. They then moved in regular troops along the side of the fell, till they came opposite Blakehills, when they went over the mountain. Then they described a kind of curvilinear path upon the side of the fell, and both these first and last appearances were bounded by the top of the mountain. "Frequently the last, or last but one, in a troop would leave his place, and gallop to the front, and then take the same pace with the rest--a regular swift walk. Thus changes happened to every troop (for many troops appeared) and oftener than once or twice, yet not at all times alike.... Nor was this phenomenon seen at Blakehill only, it was seen by every person at every cottage within the distance of a mile. Neither was it confined to a momentary view, for from the time that Strichet first observed it, the appearance must have lasted at least two hours and a half, viz. from half past seven till the night coming on prevented further view." This interesting optical illusion--which suggests the wonderful island in the Atlantic, seen from the isles of Aran near Galway, alluded to in the 'Chorographical description of West, or H-Ier-Connaught', of R. O'Flaherty--was caused by the peculiar angle of the light from the setting sun, the reflection of the water of the Solway, and the refraction of the vapour and clouds above the Solway. These aerial and visionary horsemen were being exercised somewhere above the Kirkcudbright shore. It was not the first time the phenomenon had been seen within historic times, on the same fell-side, and at the same time of year. Canon Rawnsley writes to me,