386 THE POPULAR SCIENCE MONTHLY. 



outlines, and as far as our present purposes require. It assumes nothing, 

 supposes nothing ; but, from thousands of actual and actually recorded 

 observations, presents the phenomena of spiral currents of air seeking 

 a common centre of depression, and, in the attempt to find that centre, 

 acquiring a vorticose or rotatory motion. The direction of this rota- 

 tion Mr. Redfield found to be uniformly, in our hemisphere, contrary 

 to that of the hands of a watch, with its face turned upward ; and, in 

 the Southern Hemisphere, the rotation is with those hands, or with the 

 sun in its diurnal round. It is easy to see that, if the atmospheric 

 column, resting over any given area of the earth's surface, should, for 

 any cause, be suddenly diminished, or its pressure and intensity be 

 reduced, the gaseous fluid would rush in from all surrounding regions 

 to restore the disturbed equilibrium ; and, if the earth was not whirl- 

 ing around on its axis, every particle of the centre-seeking air would 

 'endeavor to move on the shortest, or the straight line. It is known, 

 from the principles of mechanics, that this endeavor can never strictly 

 be executed, because the axial rotation of the globe incessantly so acts 

 as to throw every body, while in motion, in our hemisphere, to the 

 right of the line on which it is moving, no matter whether that line 

 be from east to west, north to south, or at any conceivable angle with 

 the meridians or the equator. Obeying, in part, this tangential im- 

 pulse, every particle of wind must take up a resultant motion. If it 

 begins to blow toward the depressed centre of the storm as a north 

 wind, it trends to the west, and is felt as a northeaster ; if it begins 

 as a south wind, it diverges as a southwester ; if as an east wind, it 

 becomes a southeaster ; and, if as a west wind, it soon changes into 

 the boreal northwest wind. 



It has often been asked whether the storms of our latitudes attain 

 the immense size formerly attributed to them; and many eminent 

 writers have denied the possibility of their reaching a diameter of 

 more than two or three hundred miles. Mr. J. K. Laughton, in his 

 recently-published " Physical Geography," would have us believe that 

 cyclones " do not attain the enormous magnitudes which have been 

 assigned them." But this opinion rests merely upon conjecture, not 

 yet upon a correct physical theory. 



It is a well-known fact that the monsoons generated on the central 

 plateau north of the Himalaya Mountains, and the whole system of 

 Asiatic wet monsoons, may be regarded as an immense and prolonged 

 cyclone ; and extend their " backing " influence into the Indian 

 Ocean, and reach far to the south, through more than forty degrees of 

 latitude (a radius of 2,500 geographical miles), and from the 69th to the 

 140th meridian of east longitude, far out into the Pacific, beyond the 

 Bonin and Ladrone Islands, southeast of Japan. The whole system 

 of wet monsoons may also be justly regarded as a grand cyclone, 

 whose centre is stationary over the heated plains of Central Asia, 



