Wordsworth's philosophical allegiances as articulated in "The Prelude" and in such shorter works as "Lines written a few miles above Tintern Abbey" have been a source of critical debate. It was long supposed that Wordsworth relied chiefly on Coleridge for philosophical guidance, but more recently scholars have suggested that Wordsworth's ideas may have been formed years before he and Coleridge became friends in the mid-1790s. In particular, while he was in revolutionary Paris in 1792, the 22-year-old Wordsworth made the acquaintance of the mysterious traveller John "Walking" Stewart (1747–1822), who was nearing the end of his thirty years of wandering, on foot, from Madras, India, through Persia and Arabia, across Africa and Europe, and up through the fledgling United States. By the time of their association, Stewart had published an ambitious work of original materialist philosophy entitled "The Apocalypse of Nature" (London, 1791), to which many of Wordsworth's philosophical sentiments may well be indebted.