'The Ignis-Fatuus, or Will-o'-the-Wisp', 1849.
© Science Museum / Science & Society Picture Library
Detail from an engraving by Josiah Wood Whymper from 'Phenomena of Nature', published in London in 1849 for the Society for Promoting Christian Knowledge. 'In marshy and boggy places, a light is sometimes seen to hover over the ground by night, appearing from a distance like a taper gleaming from some cottage window. The light is caused by the lighting up of an inflammable gas produced by decaying animal and vegetable matter in bogs, marshes and stagnant pools. It is found that when damp soils are drained, the Will-o'-the-Wisp disappears.'