STATE AGRICULTURAL SOCIETY. 405 



make observations these storms were rotary in their character, vessels being 

 driven all around the compass in a gale, the course being from left to right. 

 Information with reference to storms between 20° south of the equator and 

 the Gulf of California is deficient. The conclusion is drawn, however, that 

 the storms on the coasts of Nicaragua, Guatemala, and Mexico, are con- 

 nected with the Gulf of Mexico, or perhaps originated there. 



NOTES ON REVOLVING STORMS. 



Diagram A — The spiral lines illustrate the circulation of the wind in a 

 tropical cyclone, northern hemisphere. In the southern hemisphere the 

 circulation takes place in the opposite direction. The diameter of the 

 area represented may vary in different storms and in different latitudes 

 from about one hundred to about eight hundred miles, and is generally 

 least in low latitudes. The air is drawn in toward the center of low 

 barometer, gradually takes up a more and more circular path as its veloc- 

 ity increases, and finally whirls around the center with hurricane force. 

 At the center is a calm spot from ten to thirty miles in diameter; this is 

 marked low, and here the lowest barometer is obtained. It will be noticed 

 how similar the motion is to that of water in a whirlpool or eddy, and very 

 naturally, as this is nothing but a gigantic whirlpool in the atmosphere, 

 and the suction or draught at the center upward instead of downward. 



The direction of the wind at any point on this diagram is the same as 

 the direction of the curve at that point, and the arrows show this direction 

 at the point where they are plotted. By plotting arrows at all points hav- 

 ing the wind from the same direction — north, for example — and joining 

 them by a dotted line, we find that this dotted line curves toward the cen- 

 ter, as shown. The angle of bearing of the center, therefore, gradually 

 decreases from about ten points at the margin to about eight points in the 

 inner whirl, where the well known "eight-point rule" becomes true. 



Diagram B — Here the dotted lines are drawn from each wind arrow at 

 the margin to the center, in the way explained above, so that to find the 

 direction of the wind at any point, follow out the dotted line to the margin, 

 and read it there. The circles are isobars, and the barometer falls twenty 

 one hundredths of an inch as you go from one of these circles to the next 

 inner one. This illustrates very clearly the rate at which the barometer 

 falls as you approach the center; first slowly, as the broad outer ring is 

 traversed, then more rapidly. 



Near the center, where the isobars are very close together, it has been 

 known to fall an inch in fifty miles. Of course, as you recede from the 

 center, the barometer rises .20 of an inch as you pass from one isobar to 

 the next outer one, just as it fell on entering the hurricane. This diagram 

 involves as much of our latest knowledge of cyclones as can be safely used 

 as a general guide, and extends out beyond the regions where the barome- 

 ter is falling rapidly and the wind and sea have become violent. These 

 diagrams and the accompanying explanations only indicate how you may 

 plot your position on the diagram, and obtain from it the probable bearing 

 and distance of the center, and the track and velocity of the storm, leaving 

 it to yourself to decide what action to take, having proper regard to the 

 strength and speed of your ship, the lay of the land, and the passage you 

 are making. 



Practical use of Diagram B: Suppose that at 4 p. m., for instance, the 

 wind is E.S.E., and the barometer .20 of an inch below the normal. Find 

 at the margin of the diagram the wind arrow marked " E.S.E.," and follow 

 the dotted line in towards the center as far as the isobar marked ".20 of 



