Blest Spirits of light! Oh! ye have not forsaken. [Guardian Angels.] This is in the Appendix to the N.Y. edition of E. Caswal’s Lyra Catholica, 1851, p. 428, as Anon. In Hymns for the Year, 1867, and others, it begins "Blest spirits of light! Ye who have not forsaken." [Rev. James Mearns, M.A.]
--John Julian, Dictionary of Hymnology, New Supplement (1907)