39 3 THE POPULAR SCIENCE MONTHLY. 



energy. All that is necessary, as we have before seen, is that an 

 initial impulse of gyration be given to a body of air. The moment 

 that this takes place by mechanical influence, and, centrifugal force 

 creates the smallest eddy or vortex, the surrounding air, already 

 highly charged with moisture, begins the process of convergence and 

 ascensional motion, followed rapidly by condensation aloft, small, 

 centrical, and upright. 



The storm-cylinder the nucleus of the hurricane originally very 

 small, is instantly enlarged and expanded by the evolution of latent heat 

 stored away in the vesicles of aqueous vapor. For some hours, as all 

 observations show to be actually the case, the incipient cyclone scarcely 

 moves, while gathering in its energies and laying tributes upon all con- 

 tiguous regions. The process continues with momentarily increasing 

 intensity, and, before the sun has made his daily circuit, the meteor is 

 formed. 



If it be asked along what parallels of latitude in our hemisphere 

 this formation takes place, the intelligent reader will at once answer, 

 Near the terrestrial circle of trade-wind interference. This, we have 

 already seen, is in summer, from the 10th to the 12th parallels of north 

 latitude. 



This slender zone of debatable ground is the battle-ground of the 

 two opposing bands of the trades. There is really no need of obser- 

 vations to tell us as much. But millions of observations attest the 

 fact. Every seaman knows it. Every meteorological writer tells the 

 same story. You have only to examine physical charts from the time 

 of Columbus and Magellan to this, to see the absolute unanimity of 

 testimony, and to discover that the hypothesis now advanced, and the 

 known facts of the case, are in perfect and minute accord. 



If it be asked whether the origin of the West-Indian gales is solely 

 due to mechanical interference, the proper reply, it would clearly ap- 

 pear, should be in the negative. As the southeast trade-wind comes 

 laden with the vapor of the southern or water hemisphere, which Dove 

 well called " the boiler " of the globe, it is met by the cold northeast 

 trade from the northern, or land hemisphere. There must be a great 

 difference in their temperatures, and consequently extensive conden- 

 sation, which, by the reasoning of Mr. Clement Ley, would, of itself, 

 explain the formation of the storm. That condensation greatly assists 

 in producing and intensifying it, cannot be doubted. In the high 

 latitudes, where the polar air-current is sometimes forced by baromet- 

 ric pressure into the southerly or equatorial current moving over the 

 warm waters of the ocean, and thus heavily vapor-laden, the conse- 

 quence is illustrated by such terrific and sudden tempests as that of 

 the Royal Charter, distinctly proved by Admiral Fitzroy to have 

 been generated between the opposite polar and equatorial currents 

 off the coast of Wales. 



But that the origin of great depression systems is solely due to 



