1. Arendt , T. 1925 Heinrich Samuel Schwabe: Der Entdecker der Sonnenfleckenperiode , Dünnhaupt, Dessau
2. Digitization of Sunspot Drawings by Staudacher in 1749 – 1796
3. Carrington , R.C. 1863 Observations of the Spots on the Sun from November 9, 1853 to March 24, 1861 made at Redhill, Williams & Norgate, London, Edinburgh
4. Sun-Spot Drawings of the Rev. Frederick Howlett and Hofrath Schwabe