Wainwright's guide to the Northern Fells reports that in 1745, an army with horsedrawn carriages was seen along the top of this hill. It took 2 hours to pass and seemed to disappear over a cliff. If you Google it, you'll find that it happened more than once. They went up to look for evidence and found no trace in the marshy ground. An army of ghosts, then: spectres.Wainwright suggests that it could have been a mirage. Mirages are due to refraction when different layers of air have different temperatures. The different temperatures mean that each layer has a different refractive index. Colder air has the higher refractive index, thus light bends towards the normal line as it passes into colder air. The classic desert mirage has the hottest air nearest the ground due to the heat of the desert sands. The light can experience total internal reflection as it comes down from the colder air above and thus bend back up towards the observer. Your brain thinks light has gone straight so it appears to you that an object is below you when it truth it is above. Yes there are clearly different temperature bands as you go up a mountain. It was Midsummer Day when the spectral army was seen which might warm the atmosphere more. But I've not experienced any mirages in my years in the mountains. We saw no ghosts.
