Old Opinions on Continental Changes--Theory of Oceanic Islands--Present and Past Distribution of Land and Sea--Zoological Regions--The Palæarctic Region--The Ethiopian Region--The Oriental Region--Past changes of the Great Eastern Continent--Regions of the New World--Past History of the American Continents--The Australian Region--Summary and Conclusion _pages 304-347_ TROPICAL NATURE, AND OTHER ESSAYS. I. THE CLIMATE AND PHYSICAL ASPECTS OF THE EQUATORIAL ZONE. The three Climatal Zones of the Earth--Temperature of the Equatorial Zone--Causes of the Uniform High Temperature near the Equator--Influence of the Heat of the Soil--Influence of the Aqueous Vapour of the Atmosphere--Influence of Winds on the Temperature of the Equator--Heat due to the Condensation of Atmospheric Vapour--General features of the Equatorial Climate--Uniformity of the Equatorial Climate in all parts of the globe--Effects of Vegetation on Climate--Short Twilight of the Equatorial Zone--The aspect of the Equatorial Heavens--Intensity of meteorological phenomena at the Equator--Concluding Remarks. It is difficult for an inhabitant of our temperate land to realize either the sudden and violent contrasts of the arctic seasons or the wonderful uniformity of the equatorial climate. The lengthening or the shortening days, the ever-changing tints of spring, summer, and autumn, succeeded by the leafless boughs of winter, are constantly recurring phenomena which represent to us the established course of nature. At the equator none of these changes occur; there is a perpetual equinox and a perpetual summer, and were it not for variations in the quantity of rain, in the direction and strength of the winds, and in the amount of sunshine, accompanied by corresponding slight changes in the development of vegetable and animal life, the monotony of nature would be extreme. In the present chapter it is proposed to describe the chief peculiarities which distinguish the equatorial from the temperate climate, and to explain the causes of the difference between them,--causes which are by no means of so simple a nature as are usually imagined.