Friedel and Meyer: La Vision de Tondale (Paris, 1907); Boswell: An
Irish Precursor of Dante (London, 1908); Cambridge History of English
Literature, vol. I, chaps, xii and xvi; Windisch: _Das Keltische
Brittannien_ (Leipzig, 1912), more especially chap. xxxvii;
Dictionary of National Biography; Gwynn: Thos. Moore ("English Men of
Letters" Series, London, 1905).