corresponding station on the Alps, the former is found. to contain much more moisture, and the leaves of the same species of plant (Saxifrage, or Salix, for instance) are invariably thicker than they are when growing in the mountainous district.

The air of the Tropics is generally hot and moist; furniture and musical instruments become unglued, and valuable violins have been known to fall to pieces in India, and the West Indies, soon after their arrival from Europe. I have already alluded to its effects upon the health.

With regard to the air in cholera epidemics, Glaisher and others have drawn attention to a peculiar blue mist which occurred in London and its neighbourhood during such an epidemic; but nothing at all satisfactory was the outcome of this observation. Early in the present century, it was noted by Figari, then Professor of Botany at Abuzabel, in Egypt,1 that during the cholera epidemic of July and August 1835, several kinds of grasses, especially Maize (Indian Corn), were killed, over large districts, by blight; and the peasants who used the leaves of these plants for their cattle, or for themselves, contracted severe illness in every case.

1 This gentleman published in 1867-8 an important paper on the cultivation of the opium poppy in Egypt. See Ann. pharmaceutique de Reveil et Paris, etc., Paris, 1868, p. 330; Sur la Culture du Pavot à Opium, etc., par Figari Bey.

constant, alternant source of production, and distribution, of cold and caloric, upon which depend the various climates, the regular, periodic, and variable winds, the zones of vegetation, the currents of the ocean, and, in fact, the whole life of the globe.

The same mysterious power, called heat, or caloric, which causes the circulation of the sap in plants, and of the blood in animals, circulates also the air of the Atmosphere, and the waters of the Earth, and keeps them in constant motion; for, as I said many years ago in a former work, " movement, like matter, is universal.” 1

The vane makes its rotation, in our hemisphere, in the same direction as the Sun, a fact which was perfectly well known in the most remote antiquity (see Thales, and other ancient philosophers, quoted by Dove, in his Law of Storms), and the reverse occurs in the Southern hemisphere.

The warm wind and the cold wind (originating, respectively, at the tropics and the poles) alternate one with the other. When the warm wind displaces the cold wind, the change commences in the higher regions of the air, and the barometer falls before the thermometer rises. When the cold wind takes the place of the warm wind, the change occurs in the lower strata of the air, and the thermometer falls before the barometer rises.

When cold air descends into warm air, fog is produced; the descending current beats down the smoke of our cities, and disperses it over the surface of the Earth. 1 Phipson, Familiar Letters, etc., The movements of plants.