an optical trap

'Here and there, dark-slated roofs giving off wisps of white smoke and the sharp-edged, silvery ditches left behind by the Couesnon's meandering streams caught the eye in an optical trap of the kind that, without our knowing why, render us irresolute and prone to reverie.'

'Balzac, from Les Chouans, 1828. As quoted in Optiques: the science of the eye and the birth of modern French fiction by Andrea Goulet, 2006.