338 Cyclones. 



this also revolves abcvut the poles. Air, therefore, drawn in- 

 wards from the circumference towards the poles (where there is 

 no motion of rotation) must, on arriving there, produce a whirl, 

 or vortex, revolving in the same direction as the earth. Every 

 particle of air, in its approach towards the centre of 

 the whirl, is, moreover, obliged to obey a certain dynamical 

 law, called the law of " conservation of areas," which requires 

 that equal areas in equal times should be described about the 

 centre. In this manner its rotation is enormously increased 

 near the centre of the whirl, and a true cyclone would be 

 produced, revolving in the same direction as the earth, or in 

 that direction which is actually observed. 



Bach pole is the most central point of the hemisphere to 

 which it belongs. The instance taken as an example is, there- 

 fore, a leading, and at the same time a typical, case of what would 

 occur generally at any point of the earth's surface situated be- 

 tween the poles. A considerable depression of the barometer 

 over any region of the earth's surface, arising from any cause, 

 is accordingly sufficient to produce a true cyclone, or eddy of 

 the wind, revolving in the same direction as the earth, or in 

 the direction indicated by the " law of storms," and blowing 

 with the greatest swiftness near the centre of the whirl. 



At the equator, where both hemispheres unite, the tendency 

 of the wind to rotate is in two opposite directions ; that 

 counteract each other ; and, as far as observations at present 

 extend, cyclones exactly on the equator are not known. 



Two instances, both of them in the southern hemisphere, 

 have occurred to verify in that hemisphere the correctness of 

 the iC law of storms." The first of these crucial instances, as 

 they may be called, and perhaps the most striking, is the case 

 of the " Chai-les Heddle," which sailed from Mauritius on the 

 19th of February, 1845, and proceeding northwards, on the 

 23rd encountered a cyclone. The ship scudded, or, in nautical 

 language, was "put before the wind." From Lour to hour, for 

 five successive days, while the vessel drove directly before the 

 wind, the courses steered and the distances run over were 

 regularly entered in the ship's log. In this time, the " Charles 

 Heddle" five times circumnavigated the centre of the cyclone, 

 performing each revolution in the same direction as the hands 

 of a watch, and at the same time was carried, with the centre 

 of the storm, 400 miles back again to the Mauritius, whence 

 she started. 



The second instance, not less interesting than the last — if 

 its very recent occurrence is considered — is the case of the 

 vessel, " Earl Dalhousie," bound for Mauritius, which entered 

 a cyclone in the "storm-tract," on the evening of the ]4th of 

 May, 1863. The "Earl Dalhousie" overtook and entered the 



