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The National Geographic Magazine 



cause of the inability of water to exist 

 in the vaporous form in considerable 

 quantities except under the action of 

 the comparatively high temperatures of 

 the thin stratum near the earth, would 

 flow far into the interior of the conti- 

 nent, and by absorbing the heat of the 

 sun during the day and restricting radi- 

 ation from the earth at night markedly 

 decrease the severity of cold waves and 

 other changes in temperature. Hence 

 it is seen that the height of mountain 

 systems and their trend relative to large 

 bodies of water and to the prevailing 

 direction of winds are important factors 

 in the causing of cold waves. 



As stated before, the air has a down- 

 ward movement in the anti-cyclone, 

 which may be so feeble as to cause only 

 a slight change in temperature at the 

 earth, or it may be active enough to 

 lower the temperature down to the frost 

 line in spring or fall, or even have such 

 energy as to cause a cold wave in winter. 

 In the latter case the air possesses such 

 intense cold at the elevation from which 

 it is drawn that, notwithstanding the 

 fact that it gains heat by compression 

 at the rate of about i degree for each 200 

 feet of descent, it is still far below normal 

 temperature when it leaches the earth. 

 Its initial temperature is so low that it 

 can contain only a minute portion of 

 water vapor ; it therefore evaporates all 

 fog or cloud as it gains in temperature 

 during its fall, and by flowing away lat- 

 erally along the earth it drives away the 

 more humid air of the lower strata. The 

 downward motion thus introduces con- 

 ditions of clearness and deficiency of 

 water vapor that promotes free radia- 

 tion and the loss of much of the heat 

 dynamically gained as well as that given 

 off by the earth to the air. It therefore 

 seems that departures from the normal 

 temperature of a time and place are the 

 result of the motions of the air below the 

 height of 10 miles. Ascending and de- 

 scending currents cease before this alti- 

 tude is reached, and it is probable that 



the temperature of this region changes 

 but little from season to season and 

 from year to year, although short-period 

 observations with the bolometer, which 

 registers changes in the amount of heat 

 that falls upon the outer limits of the 

 air, indicate that in time it possibly may 

 be necessary to modify this opinion. 



Few people realize that the cold wave 

 has an important therapeutic value. It 

 scatters and diffuses the carbonic-acid 

 gas exhaled by animal life and the fetid 

 gas emanating from decaying organic 

 matter. Its dense air not only gives 

 more oxygen with each inspiration of 

 the lungs, but the high electrification 

 that always accompanies it invigorates 

 man and all other animal life. The 

 cold north wind, if it be dry, as it 

 usually is, brings physical energy and 

 mental buoyancy in its pure but bois- 

 terous breath. 



HURRICANES 



Most of the storms that gain such a 

 velocity of gyration as to consitute hur- 

 ricanes originate in the tropics and move 

 northwestward to latitude 26 degrees to 

 32 degrees, where they recurve and move 

 toward the northeast. These are the 

 most severe of all the storms that visit the 

 North American continent. The West 

 Indies and the Philippines are the re- 

 gions wherein these forceful storms 

 originate in the greatest numbers, and 

 the commerce of all nations has profited 

 largely by the spirit that has prompted 

 the United States to establish, since 

 1898, a complete system of cable-report- 

 ing meteorological stations in both of 

 these sections, which enables a central 

 station to keep mariners advised of 

 danger. 



At times hurricanes remain several 

 days in the Gulf of Mexico or off our 

 South Atlantic coast, and the only in- 

 dication we have of their proximity is a 

 strong suction drawing the air briskly 

 over some of our coast stations toward 

 the center of the storm. Again, a 



