VANILLA, or VANILLO. See EPIDENDRUM. VAPOUR, in philosophy, the particles of bodies rarefied by heat, and thus rendered specifically lighter than the atmosphere, in which they rise to a considerable height. See EVAPORATION, DAMP, GAS, &c.
Many kinds of vapour are unfriendly to animal life, but the most noxious are those which arise from metallic substances. In the smelting and refining of lead, a white vapour arises, which, falling upon the grass in the neighbourhood, imparts a poisonous quality to it, so that the cattle which feed there will die; and in like manner stagnant waters impregnated with this vapour will kill fish. Phlogistic vapours are also extremely noxious; and hence painters, and others who are exposed to these vapours, are generally unhealthy. In some places the earth exhales vapours of a very noxious quality; such as the Grotto del Cani, and other places in Italy, where a mephitic vapour constantly hovers over the surface of the ground, proving instantly fatal to such animals as are immersed in it. But the most formidable kind of vapours are those which issue from the mouths of volcanoes, and which seem to be a combination of all others, joined to such a quantity of electric matter as to produce the greatest mischiefs. In some parts of the world there have been instances of people killed, and almost torn to pieces, by a vapour suddenly bursting out of the earth under their feet.
Of the aqueous vapour raised from the earth by the sun's heat are formed the clouds; but though these are commonly at no great height from the earth, we cannot from thence determine the height to which the vapours ascend. Indeed, considering the great propensity of water, and even quicksilver, to evaporate in the most perfect vacuum we can make, it is by no means probable that any limit can be fixed for this ascent.