Page:Popular Science Monthly Volume 38.djvu/151

Rh civilization in Europe, but linger through Mohammedan barbarism in Africa. There is abundant evidence of the former existence of these and other large mammals of tropical Africa in France, Germany, and Greece. The original fauna of Africa, of which the lemur is the distinctive type, is still preserved in Madagascar, which once formed part of Africa. The trout is found in all the snow-fed rivers that fall into the sea, but not in Palestine south of the Lebanon, or in Egypt, or the Sahara. The freshwater salmonoid is a European type often found in the Atlas. There are newts and tailed batrachians in every country round the sea, again excepting Palestine, Egypt, and the Sahara.

Economic Plants of Colombia.—A report of the British Foreign Office names a large variety of important economical plants as successfully cultivated in Colombia. The principal crop is maize; next to it is sugarcane, which is most used for making sugar, while large quantities of it are employed for making aguardiente and rum in the hot country, and chicha, another drink, in the cold country. The plant ripens in one year in the hot country, and in a year and a half in the cold country. Cacao is largely raised in the hot country on the slopes of the mountains, on newly disforested land, at an elevation of from one thousand to three thousand five hundred feet. It is the most paying crop in the country when once established, but very difficult and expensive to take care of in the earlier years of its growth. For planting the upland rice, the ground is "prepared" by turning cattle into the field after the first rains to tread up the ground and destroy the grasses. They are again turned in and driven round, after the seed has been sown, to tread it into the ground, after which no further attention is paid to the crop till the harvest. The potato forms the chief food of the country. It is very productive, and is cultivated in two principal varieties—the criollas, which are red-skinned, and yellow or orange-colored inside, and the ordinary white potato. It also grows wild in the mountains. The largest and best crops are raised on savannas on the mountain-sides at heights of more than nine thousand feet. The production has greatly decreased since the potato disease attacked the crops in 1865. Tobacco is grown on a large scale in four districts and on a small scale all over the country. Other cultivated plants are plantains, which form an important food and are very productive; manioc, which is used as a vegetable or made into bread; vegetable ivory palm; Carlodovica palmata, from which the Panama hats are made; coca; coffee, the production of which is increasing and which is taking the place of cinchona bark as the chief article of export; American aloe, which grows wild everywhere and is valuable for its fibers; and cinchona. Pineapples, oranges, mangoes, cherimozas, and other native fruits grow very abundantly and spontaneously, and are so cheap that, except in the immediate neighborhood of a market, few people take the trouble to pick them.

The Start of a Bird's Flight.—The mechanism of the starting of a bird's flight, as studied by instantaneous photography, is thus described by Professor Marey: When the bird is not yet in motion, the air which is struck by its wings presents, in the first instance, a resistance due to inertia, then enters into motion, and flies below the wing without furnishing to it any support. When the bird is at full speed, on the contrary, its wing is supported each moment upon new columns of air, each one of which offers to it the initial resistance due to its inertia. The sum of these resistances presents to the wing a much firmer basis. One might compare a flying bird to a pedestrian who makes great efforts to walk on a shifting sand, and who, in proportion as he advances, finds a soil by degrees firmer, so that he progresses more swiftly and with less fatigue. The increase of the resistance of the air diminishes the expenditure of labor; the strokes of the bird's wing become, in fact, less frequent and less extended. In calm air, a sea-gull which has reached its swiftest expends scarcely the fifth of the labor which it had to put forth at the beginning of its flight. The bird which flies against the wind finds itself in still more favorable conditions, since the masses of air, continually renewing themselves, bring under his wings their resistance of inertia. It is, then, the start which forms the most laborious phase of the flight. It has long been observed that birds employ all