Although we customarily think of Forbes as being primarily a glaciologist, he came earlier to public notice as the author of a lengthy series of articles on the volcanic phenomena of Naples. His major topics included Vesuvius, Somma, Herculaneum, Pompeii, Stabiae, the supposed Temple of Jupiter Serapis, the Solfatara, the Phlegraean Fields, Monte Nuovo, Procida, Ischia, and related phenomena. Although much of what he says is no longer surprising, some of his opinions (or those he opposes) perhaps are. Ami Boué, in France, spoke well of Forbes's Neapolitan observations, as did Charle Lyell in the first edition of Principles of Geology (1830-1833).