Volcanic rocks from Mount Vesuvius, 1779.

Hand-coloured etching by Peter Fabris (active 1768-1779). One of five illustrated plates from the 1779 supplement to William Hamilton's study of Italian volcanoes, 'Campi Phlegraei' (published in Naples, 1776). Images show (1) new lava pores, (2, 3) solid glas in centre of lava, (4) scoria of vitrified lava, (5, 6) scoria and (7) vitrified matter. Based on letters to the Royal Society, the book was a more precise study of volcanoes than had previously existed, illustrating Hamilton's claim that volcanoes are creative natural forces.