Humboldt remembers with gratitude the assistance rendered by le Duc to himself and his friends and collaborators, [Louis Joseph] Gay-Lussac and [Christian Leopold von] Buch. He hopes that M. Brongniart, 'l'homme célèbre', who wishes to visit Vesuvius and the lava flows of Ischia [a volcanic island near Naples], will be afforded similar kindnesses. Alexandre Brongniart (1770-1847) was a French chemist, mineralogist, and zoologist, who collaborated with Georges Cuvier on a study of the geology of the region around Paris. In 1800 he was appointed director of the porcelain manufactory at Sèvres, a position he held until his death 47 years later. Alexander von Humboldt (in full, Friedrich Wilhelm Heinrich Alexander, Freiherr [Baron] von Humboldt) was a major figure in the classical period of physical geography and biogeography. His book 'Kosmos' (1845) made a valuable contribution to the popularization of science. Numerous species and geographical features have been named after him, not least the Humboldt Current off the west coast of South America (biographical details courtesy of Encyclopaedia Britannica and Wikipedia, both online).