Page:Popular Science Monthly Volume 9.djvu/658

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632
THE POPULAR SCIENCE MONTHLY.

lated by the plant in the free state—determined to apply infusorial earth to land sown in wheat, and afterward with the microscope to search for the siliceous shields of diatomaceæ in the straw. Of course, if these were to be found occurring in the plant with the same forms which they have in the infusorial earth, it is plain that they must have been taken up by the plant and distributed through its system unaltered. The event fully justified this conclusion. The straw having been treated with nitric acid, the siliceous residuum was placed on the field of the microscope, and was seen to consist wholly of the siliceous shields of diatomaceæ the same as found in the infusorial earth, excepting that the larger disks in their perfect form were absent—evidently because these disks were not sufficiently minute to enter the root-capillaries. The result of these investigations shows the necessity of finely-divided silica in the soil; also, that simple or compound silicates are useless as fertilizing agents.

 

Forestry.—The first of a series of papers on "European and American Forestry," now appearing in the Penn Monthly, contains a brief history of "Deforestation," or devastation of forests, in the Old World. The subject is one that nearly concerns the inhabitants of the United States, where the process of deforestation advances with unparalleled rapidity. Among the many instances quoted by the author of the evils consequent on the denudation of woodlands is that of Sicily, once the granary of Rome, now almost a waste from the effects of forest devastation. The island has scarcely a stream that lasts through the summer, and few perennial springs. The soil has suffered deplorably for want of sufficient irrigation. Greece, in common with Asia Minor, has been shorn of its original forests, and its characteristic feature is represented in steppes and unproductive barren wastes. Of Spain it may be said that at one time one-fifth of its surface was forest; now the proportion is only nine per cent. Indifferent portions of the country noble forests still exist; but, on the whole, the destruction of the useful woods has been indiscriminate and improvident, and Spain, like all other countries, has suffered under the abuse of that universal law according to which soil and climate depend on the extent of forest-land.

 

Air-Bags for raising Ships.—Prof St. Claire, of Edinburgh University, in 1785 proposed the use of air-bags for the purpose of raising sunken ships. In 1864 airbags were first practically applied for raising a steamer sunk in the lake of Boden; in this case the bags, owing to some defect, gave way. The Alexandrovsky system, perfected some ten years ago, has already rendered good service to the Government and commerce of Russia on several occasions. The bags adopted in the Russian Navy, as we learn from Engineering, are, when inflated, of cylindrical form, measuring twelve feet in diameter and twenty feet in length. They are composed of three layers of the thickest canvas saturated with India-rubber. Their lifting power averages sixty tons. In order to lift a vessel, several chains are drawn by divers under her bottom, and air-bags attached to the ends of each of them as near the ship's bottom as possible: the bags, being inflated by means of air-pumps, cause the ship to rise. Before pumping air into the bags, all the chains are connected in a transverse direction, so as to form one system, thus preventing the pairs of bags from sliding off from beneath the hull of the ship. As the vessel rises the surrounding water-pressure decreases, and the excess of air passes out through safety-valves.

 

Night-Habits of Fish.—Mr. W. Saville Kent had in the Manchester Aquarium a number of young herrings, which were so tame as readily to take their prepared food from the hand of a keeper. But a large number of the fishes were found dead each morning, a fact which seemed inexplicable, considering their quiet behavior during the day. A night inspection, however, revealed the cause of this rapid destruction. It was found that the nocturnal movements of the herring, at least in confinement, are altogether different from their movements in daylight. In the latter case, these movements are quiet and uniform, the fish swimming around their tank in one shoal and one continuous stream. At night,