« EelmineJätka »
cultivated country. The open sandy country with scattered trees and shrubs or occasional thickets, which is found at Santarem and Montc-Alegre on the lower Amazon, are examples, as well as the open cultivated plains of Southern Celebes ; but in both cases the forest country in adjacent districts has a moister and more uniform climate, so that it seems probable that the nature of the soil or the artificial clearing away of the forests, are important agents in producing the departure from the typical equatorial climate observed in such districts. The almost rainless district of Ceara on the North-East coast of Brazil and only a few degrees south of the cquator, is a striking example of the need of vegetation to react on the rainfall. We have here no apparent cause but the sandy soil and bare hills, which when heated by the equatorial su produce ascending currents of warm air and thus prevent the condensation of the atmospheric vapour, to account for such an anomaly; and there is probably no district where judicious planting would produce such striking and beneficial effects. In ('entral India the scanty and intermittent rainfall, with its fearful accompaniment of famine, is no doubt in great part due to the absence of a sufficient proportion of forest-covering to the earth's surface; and it is to a systematic planting of all the bill tops, elevated ridges, and higher slopes that we can alone look for a radical cure of the evil. This would almost certainly induce an increased rainfall ; but even more important and more certain, is the action of forests in checking evaporation from the soil and causing perennial springs to flow, which may be collected in
vast storage tanks and will serve to fertilise a great extent of country ; whereas tanks without regular rainfall or permanent springs to supply them are worthless. In the colder parts of the temperate zones, the absence of forests is not so much felt, because the hills and uplands are naturally clothed with a thick coating of turf which absorbs moisture and does not become overheated by the sun's rays, and the rains are seldom violent enough to strip this protective covering from the surface. In tropical and even in south-temperate countries, on the other hand, the rains are periodical and often of excessive violence for a short period; and when the forests are cleared away the torrents of rain soon strip off the vegetable soil, and thus destroy in a few years the fertility which has been the growth of many centuries. The bare subsoil becoming heated by the sun, every particle of moisture which does not flow off is evaporated, and this again reacts on the climate, producing long-continued droughts only relieved by sudden and violent storms, which add to the destruction and render all attempts at cultivation unavailing. Wide tracts of fertile land in the south of Europe have been devastated in this manner, and have become absolutely uninhabitable. Knowingly to produce such disastrous results would be a far more serious offence than any destruction of property which human labour has produced and can replace; yet we ignorantly allow such extensive clearings for coffee cultivation in India and Ceylon, as to cause the destruction of much fertile soil which generations cannot replace, and which will surely, if not checked in time, lead to the deterioration of the climate and the permanent imporеrishment of the country. 1
Short Twilight of the Equatorial Zone.- One of the phenomena which markedly distinguish the equatorial from the temperate and polar zones, is the shortness of the twilight and consequent rapid transition from day to night and from night to day. As this depends only on the fact of the sun descending vertically instead of obliquely below the horizon, the difference is most marked when we compare our midsummer twilight with that of the tropics. Even with us the duration of twilight is very much shorter at the time of the equinoxes, and it is probably not much more than a third shorter than this at the equator. Travellers usually exaggerate the shortness of the tropical twilight, it being sometimes said that if we turn a page of the book we are reading when the sun disappears, by the time we turn over the next page it will be too dark to see to read. With an average book and an average reader this is certainly not true, and it will be well to describe as correctly as we can what really happens.
In fine weather the air appears to be somewhat more transparent near the equator than with us, and the intensity of sunlight is usually very great up to the moment when the solar orb touches the horizon. As soon as it has disappeared the apparent gloom is proportionally great, but this hardly increases perceptibly during the first ten minutes. During the next ten minutes however it becomes rapidly darker, and at the end of
For a terrible picture of the irreparable devastation caused by the reckless clearing of forests see the third chapter of Mr. Marsli's work The Ear!h as Jlodified by luman Action.
climbers, even more than all other plants, is upward towards the light. In the shade of the forest they rarely or never flower, and seldom even produce foliage ; but when they have reached the summit of the tree that supports them, they expand under the genial influence of light and air, and often cover their foster-parent with Llossoms not its own. Here, as a rule, the climber's growth would cease ; but the time comes when the supporting tree rots and falls, and the creeper comes with it in torn and tangled masses to the ground. But though its foster-parent is dead it has itself received no permanent injury, but shoots out again till it finds a fresh support, mounts another trce, and again puts forth its leaves and flowers. In time the old tree rots entirely away and the ('rceper remains tangled on the ground. Sometimes branches only fall and carry a portion of the creeper tightly stretched to an adjoining tree; at other times the whole tree is arrested by a neighbour to which the creeper soon transfers itself in order to reach the upper light. When by the fall of a branch the creepers are left hanging in the air, they may be blown about by the wind and catch hold of trees growing up beneath them, and thus become festooned from one tree to another. When these accidents and changes have been again and again repeated the climber may have travelled very far from its parent stem, and may have mounted to the tree tops and descended again to the earth several times over. Only in this way does it scem possible to explain the wonderfully complex manner in which these climbing plants wander up and down the forest as if guided by. the strangest caprices, or how they become so crossed and tangled together in the wildest confusion.
sunshine lights up the glorious vegetation of the tropics, and realises all that the magic art of the painter or the glowing words of the poet, have pictured as their ideals of terrestrial beauty.
The aspect of the Equatorial IIcarens.— Within the limits of the equatorial zone the noonday sun is truly vertical twice every year, and for several months it passes so near the zenith that the difference can hardly be detected without careful observation of the very short shadows of vertical olijects. The absence of distinct horizontal shadows at noon which thus characterises a considerable part of the year, is itself a striking phenomenon to an inhabitant of the temperate zones; and equally striking is the change aspect of the starry heavens. The grand constellation Orion, passes vertically overhead, while the Great Bear is only to be seen low down in the northern heavens, and the Pole star either appears close to the horizon or las altogether disappeared according as we are north or south of the cquator. Towards the south the Southern Cross, the Magellanic clouds, and the jet-hack “coal sacks” are the most conspicuous objects invisibile in our northern latitudes. The same cause that brings the sun overhead in its daily march equally affects the planets, which appear high up towards the zenith far more frequently than with us, thus affording splendid opportunities for telescopic observation.
Intensity of Meteorological Phenomena at the Equator. -The excessive violence of meteorological phenomena generally supposed to be characteristic of the tropics is mot by any means remarkable in the equatorial zone. Electrical disturbances are much more frequent, but not