4:22 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



of meteorology will enable lis to warn the ships in our Gulf 

 ports, as well as those of Cuba, of the approach of every hurricane 

 or tornado that visits those regions. 



791. The changing of the wind in a cyclone. — But, returning to the 

 cyclone theory : though the wind be blowing around in spirals 

 against the hands of the watch, yet, from the fact that the centre 

 about which it is blowing is also travelling along, the changes of 

 the wind, as observed by a vessel over which the storm is 

 passing, will not, under all circumstances, be against the sun in 

 the northern, or ivith the sun in the southern hemisphere. The 

 reason is obvious. This point is worth studying, and any one 

 who will resort to " moving diagrams " for illustration will be 



repaid with edification. Piddington's 

 horn cards are the best; but let those 

 who have them not cut a disc of paper 

 of any convenient diameter, say 2^ 

 inches, and then cut out a circle of 2 

 inches from the middle ; this will leave a 

 ring half an inch broad upon which to 

 draw arrows representing the course of 

 the wind. Suppose them to be drawn 

 for the northern hemisphere, as in the 

 annexed diagram ; lay the paper ring on the chart : suppose the 

 ship to be in the N.E. quadrant of the storm, which is travelling 

 north, the centre of the storm will pass to the west, but the wind 

 will change from S.E. to S., and so on to the west, with the hands 

 of a watch, though it be revolving about the centre against the 

 hands of a watch ; still the rule for finding the direction of the 

 centre holds good : Face the wind, and the centre in the northern 

 hemisphere will be to the right; in the southern, to the left. 



792. TJie wind stronger on one side than the other. — Suppose that 

 in the case before us the storm is travelling to the north at the 

 rate of 20 miles the hour, and that the wind is revolving around 

 the centre also at the rate of 20 miles the hour : when the vortex 

 bears west of the shij:), the wind will be south. It is going 20 

 miles to the north with the body of the storm, and 20 miles 

 around the centre ; total force of the wind, 40 miles an hour on 

 the east side. Now imagine yourself on the other side, that is, 

 that you are in the north-west quadrant, and that the storm is 

 travelling due north as before ; the vortex will pass east of you, 

 when the wind should have changed from N.E. to north, turning 



