THE ANNALS AND MAGAZINE OF NATURAL HISTORY, No. 57. MAY 1842. XXII. — ThePhysical Agents of Temperature, Humidity, Light, and Soil, considered as developing Climate, and in connexion with Geographic Botany, By Richard Brinsley Hinds, Esq., Surgeon R.N. It is our present intention to institute some inquiries into the circumstances of climate and physical agents in connexion with the distribution of the vegetation of our globe ; and as these are the results of several agents acting in co-operation as well as individually, and their mutual influence embraces much complexity, it will be advisable to regard them sepa-rately under the heads of, 1. Temperature, 2. Humidity, 3. Light, 4. Soil. I. Temperature. Climate is the great presiding agent over the flora of the world, and, as modified by external circumstances, stamps its characters on the productions. Climates vary a good deal in circumstances, according to the latitude. In the belt which borders on the equator, and is confined within the tropics, the annual climate is of the simplest kind, and is divided into a wet and a dry season. The temperature throughout the year varies but little, and a ver}^ trifling range takes place in the barometer. The seasons alternate with surprising regularity, the inhabitants looking forward to the accession or departure of the rains almost to a day. In receding north and south from the equator, the wet and dry seasons take place at dif-ferent periods of the year ; when the sun enters the northern hemisphere, the wet or rainy season of that side commences, and it is then the time of the dry season in the southern he-misphere. The reverse happens as the sun occupies the other side of the equator. Thus two tropical climates exist, very similar to each other, and chiefly differing in the circumstance that the seasons occur at opposing periods. These are the outlines of tropical cUmates as existing over continents ; some modifications take place over the large oceans. Near the equator, and to about 7° N. lat,, a pecuHar region exists ; the trade winds do not advance so far, and light baffling winds, Ann, ^ Mag. N. Hist. Vol Ax. N
BioStor
