Page:Popular Science Monthly Volume 46.djvu/588

572 of Nature is that in which she converts apparently inaccessible and unutilizable material into inexhaustible supplies for every industry of man. A wonderful example of this is found in the littoral feeding grounds. There is a bench of land under the sea skirting every shore and reaching under all estuaries. It is not deep. Indeed, it is the connecting link between the land and the profound sea. Upon this plateau the débris of the fertile lands and of the fresh waters is daily poured, and myriads of the lower plants and animals are developed. Here are nourished cod, shad, herring, salmon, oysters, clams, and so on. The fish after attaining maturity actually swim up to men's doors to be captured. Also upon this feeding ground are nourished the sea mammals which have been indispensable to the life and happiness of our northern aborigines. It is true that every useful plant is converted by Nature out of material which men can not use. Long before Texas cattle were bred in one place and driven hundreds of miles to market Nature reared fish and walrus upon her enormous pasture lands under the sea and drove them to market herself.

Effects of Occupation on Eyesight.—The effects of certain occupations on eyesight are manifested, according to Mr. Simeon Snell, who has made a study of the subject, in a variety of ways. Workers in India-rubber factories are troubled by the fumes of bisulphide of carbon, which is used in the vulcanizing process. The vapor of this substance was formerly employed as an irritant of the conjunctiva and a promotive of abundant lachryimationlacrimation [sic], and it tends to produce amblyopia. Amblyopia, or dullness of vision, is brought about in the manufacture of explosives by dinitro-benzyl. While the toxic action of tobacco when chewed seems to be established, the assertion that persons working in tobacco factories are subject to disorders of vision has not been confirmed. The prejudicial action of lead is well known, but to the usual experiences in the matter Mr. Snell adds the curious instance of amblyopia produced among the file-cutters of Sheffield by inhalation of the particles of lead that fly off from the lead bed on which the file is laid to be struck. The statements that glass-blowers are subject to cataract from exposure of their eyes to the intense heat and light of the furnaces are not supported by the later observations. Mr. Snell has found that men can look at metal in the furnace with comparative ease, so long as its temperataretemperature [sic] is not greatly above 2,000º F.; but when it approaches 3,000º F. they have to wear colored glasses. At cast-iron furnaces, where the heat of the metal is between 1,800º and 2,000º, the men take no special precautions; but the heat of molten steel is between 2,700º and 2,800º, while the heat of the gases in the furnaces would be about 200º or 300º more, and the men in attendance have to wear dark-blue glasses to protect their eyes. The heat of the metal in the Bessemer process is greater still, increasing to 3,000º or 3,200º, but the metal does not have to be so long or so carefully watched as in the Siemens furnace. In none of these cases has Mr. Snell been able to associate any deep or superficial eye lesion as the result of exposure to intense light and heat. Exposure to the light employed in electric welding causes sharp conjunctivitis, with great pain and tear-shedding, and, if it be allowed to enter the eye, optic neuritis, with retinitis and a central scotoma in the vision. The effects are due to the chemical rays, and the men are obliged to use screens made of dark ruby, non-actinic glass.

Geological Work of the Atmosphere.—Believing that too little attention has been given by American geologists to the work performed by the atmosphere in erosion, transportation, and sedimentation. Prof. J. A. Udden, of Augustana College, has considered the subject in a brief paper. He begins by assuming that as an agent of erosion air is far less efficient than water—because of its small weight, it being only as heavy as water, and because it exerts no wave motion on the surface of the earth. The erosive action of wind therefore becomes important only in certain localities, under the favoring conditions of a dry climate and a topography of abrupt and broken reliefs. Since the speed of the wind is lowest near the surface of the ground, materials to be transported any considerable distance by the atmosphere must be by some means lifted through and over this zone of low velocity. This condition is furnished by whirlwinds and reliefs which cause