On July 12, 1819, William Howard (1793-1834) and Jeremiah van Rensselaer (1793-1871) made the first American ascent of Mont Blanc. Note the use of the rope while crossing the crevasse of the Glacier de Boissons with a ladder. A similar pen and ink sketch of this scene accompanies a manuscript version of his journey written ten days after the ascent, now in the Princeton University Library Manuscripts Collection.
Source: William Howard, Narrative of a journey to the summit of Mont Blanc, made in July, 1819 (Baltimore, 1821), frontispiece. *AC8 H8374 821n, Houghton Library, Harvard University; http://id.lib.harvard.edu/aleph/005776975/catalog
William Howard, Mont Blanc, belay