George Forbes, “Additional Note on the Ultra-Neptunian Planet, whose existence is indicated by its action on Comets” read to the Royal Society of Edinburgh, 1901., 1901., Acc.13827/1069. Further papers of the Forbes and Stuart Forbes families of Fettercairn and Pitsligo, with papers of the Trefusis family relating to Fettercairn and Pitsligo., Acc.13827/1-1103. National Library of Scotland Archives and Manuscripts Division. https://nlssb.as.atlas-sys.com/repositories/2/archival_objects/134748 Accessed September 23, 2024.