572 



THE POPULAR SCIENCE MONTHLY. 



of Nature is that in which she converts ap- 

 parently inaccessible and unutilizable mate- 

 rial 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 skirt- 

 ing every shore and reaching under all estu- 

 aries. It is not deep. Indeed, it is the 

 connecting link between the land and the 

 profound sea. Upon this plateau the debris 

 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 feed- 

 ing 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 Occnpation 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 bi- 

 sulphide of carbon, which is used in the 

 vulcanizing process. The vapor of this sub- 

 stance was formerly employed as an irritant 

 of the conjunctiva and a promotive of abun- 

 dant lachryiuation, and it tends to produce 

 amblyopia. Amblyopia, or dullness of vision, 

 is brought about in the manufacture of ex- 

 plosives by dinitro-benzyl. While the toxic 

 action of tobacco when chewed seems to be 

 established, the assertion that persons work- 

 ing in tobacco factories are subject to dis- 

 orders 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 ambly- 

 opia produced among the file-cutters of Shef- 

 field 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 sup- 

 ported by the later observations. Mr. Snell 

 has found that men can look at metal in the 

 furnace with comparative ease, so long as its 

 temperatare is not greatly above 2,000 F. ; 

 but when it approaches 3,000 F. they have 

 to wear colored glasses. At cast-iron fur- 

 naces, where the heat of the metal is between 

 1,800 and 2,000, the men take no special 

 precautions ; but the heat of molten steel is 

 between 2,700 and 2,800, while the heat 

 of the gases in the furnaces would be about 

 200 or 300 more, and the men in attend- 

 ance have to wear dark-blue glasses to pro- 

 tect their eyes. The heat of the metal in 

 the Bessemer process is greater still, in- 

 creasing to 3,000 or 3,200, 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. 



Geologieal 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 con- 

 sidered the subject in a brief paper. He be- 

 gins by assuming that as an agent of erosion 

 air is far less efficient than water because of 

 its small weight, it being only g-fj as heavy 

 as water, and because it exerts no wave mo- 

 tion 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 con- 

 siderable distance by the atmosphere must be 

 by some means lifted through and over this 

 zone of low velocity. This condition is fur- 

 nished by whirlwinds and reliefs which cause 



