Abstract
The behaviour of a mass of molten but cooling igneous rock under moderate pressure may be compared to that of liquid cupelled silver, which at a certain temperature can no longer retain the oxygen, many times its volume, that it has occluded. Thus, during the submarine eruption off the island of Pantelleria in 1891, blocks of lava that swam for a while on the surface of the sea exploded with violence. Chilling by contact with sea-water had occasioned exactly what Lowthian Bell observed to happen on the sudden cooling of masses of slag by contact with water. There was a discharge within the set outer envelope, at something near a red heat, of previously dissolved water and gases, converting the floating ejectamenta into a species of bombs.