circumstances arising from the influence of causes which are local and as yet unknown. The monsoons are more valuable as auxiliaries to commerce than the trade winds, owing to the change in their direction, for a ship may proceed to a distant port with one monsoon and be aided on its return by its successor. 3. _Land and sea breezes._ A line in one of our popular songs, “How sweetly the breeze blows off the shore,” refers to the wind which begins at evening to blow from the coasts situated between and near the tropics: and an equally grateful breeze blows by day from the sea to the shore in those warm climates. The inequality of the solar action on the land and water, together with the tendency of the atmosphere to preserve an uniform density, is the cause of these periodically shifting currents. During the day the land acquires a temperature higher than that of the ocean, and the air over it is therefore rarefied and ascends, and the cooler air from the sea glides in to fill the partial vacuum produced. At night, the land rapidly cools with the atmosphere over it, but the sea and the air in connection with it retain a nearly equal temperature, in consequence of which, the colder and heavier land-air displaces the less dense or lighter air over the water, and a wind from the shore is created. The smoke of Vesuvius beautifully exemplifies this diurnal change in the direction of the atmospheric currents along the shore, its long tail stretching landward for a few hours, and then veering round to seaward. In the Mediterranean and the West Indies, the land breeze usually begins at six or seven o’clock in the evening, and blows until eight in the morning, when the sea breeze begins, increasing till mid-day, and gradually dying away in the afternoon, a period of stillness occurring between the changes, as between the ebbing and flowing of the tide. The sea-breeze of the Mediterranean in summer is said to be perceptible sometimes as far north as Norway. These draughts of the cool air of the ocean are important benefactions to various countries, where the heat would otherwise be insupportable. Along the coast of Malabar, the alternate breezes are powerfully felt, the land wind extending in summer a considerable distance out to sea, redolent with the roses and spices of the shore. Though the land and sea breezes are most sensible in tropical countries, yet in far remote latitudes, and especially around lakes, the same diurnal shifting in the direction of the wind is experienced. The change of temperature in the air over a spacious lake, caused by the succession of day and night, has been computed to be about thirty times less than that which takes place in the atmosphere of the surrounding land—the air over the land being much more heated during the day, and much less heated during the night, than that over the lake—an inequality of temperature which necessarily occasions a breeze from the lake by day, and toward it by night.