Photographic portrait of Robert W. Bunsen, Gustav Kirchhoff, and Henry E. Roscoe. In the book Roscoe explains that the photograph was taken during a visit of Bunsen and Kirchhoff to Manchester while Roscoe was chair of chemistry at Owens College, Manchester. Roscoe knew Kirchhoff and Bunsen from his time spent in Heidelberg studying under Bunsen.
Roscoe, Henry E. (Henry Enfield). “Bunsen, Kirchhoff, and Roscoe.” Paper. The Life & Experiences of Sir Henry Enfield Roscoe ... Written by Himself. London, England: Macmillan Company, 1862–1906. https://digital.sciencehistory.org/works/7m01bm800.