1888.] for handling Ships in the Southern Indian Ocean. 315 



ships, and correlates the whole with the modern methods of meteor- 

 ology. 



As an example, a hurricane is taken which blew near Mauritius on 

 February 11, 12, and 13, 1861, and the history of every ship to which 

 the rules nrght apply is minutely investigated. The result, dividing 

 Meldrum's rules shortly into three parts, is as follows : — 



Rule 1. Lie to with increasing south-east wind till the barometer 

 has fallen 6-10ths of an inch. Seven cases, rule right in every case. 



Rale 2. Run to north-west when the barometer has fallen 6-10ths 

 of an inch. Three eases, two failures, one success. 



Rule 3. Lie to with increasing north-east or east wind and a falling 

 barometer. Seven cases, rule right in every instance. 



Rule 2 was exceptionally unfortunate in this the path of the 



central vortex moved in a very uncommon and irregular manner. At 

 the same time, in any case, it appears to be about equally hazardous to 

 follow this rule or to remain hove to. 



The following statements are then examined in detail : — 



The shape of all hurricanes is usually oval, not circular. An elabo- 

 rate examination is made of hurricanes on 60 different days, in 18 

 different tropical cyclones in various parts of the world, with the 

 following results : — 



1. Out of 60 days, cyclones were apparently circular on only four 

 occasions, and then the materials are very scanty. 



2. The shape was oval on the remaining 56 days, but the ratio of the 

 longer and shorter diameter of the ovals very rarely exceeded 2 to 1. 



3. The centres of the cyclones were usually displaced towards some 

 one side. No rule can be laid down for the direction of displacement, 

 and in fact the direction varies during the progress of the same 

 cyclone. The core of a hurricane is nearly as oval as any other 

 portion. 



4. The longer diameter of the ovals may lie at any angle with 

 reference to the path of the cyclone ; but a considerable proportion lie 

 nearly in the same line as the direction of the path. 



5. The association of wind with the oval form is such that the 

 direction of the wind is usually more or less along the isobars, and 

 more or less incurved. This is the almost invariable relation of wind 

 to isobars all over the world. 



From an examination of the whole it is proved conclusively that 

 no rule is possible for determining more than approximately the position 

 of the central vortex of a cyclone by any observations at a single station. 



The relation of a hurricane to the south-east trade is then discussed, 

 and it is shown that there is always what may becalled " a belt of inten- 

 sified trade wind" on the southern side of a cyclone, while the hurri- 

 cane is moving westwards. In this belt a ship experiences increasing 

 south-east winds and squalls of rain, with a falling barometer, but is not 



vol. xliv. 2 B 



