METEOROLOGY. 479 



if this centre should have a diameter of 50 or 60 miles, roniid which the storm ia 

 revolving, our first care must be to ascertain how this point or centre bears from 

 us, in order to guide our future manoeuvres. Now, as the Monocacy on the 5tU 

 of January was, according to her log, in latitude 32° 15' south, and longitude 

 47° 45' east, the wind marked as E.SE., the centre of every common wind would 

 lay ,^ according to proved and established rules of storm's, to the E. by N. or 

 E.NE. In the remarks on January 5th it is said, clouds accumulating,"^ cloudy 

 and damp, moderate breeze from SE. by E., sent up foretopmast; from 4 to 6, 

 squally and damp, heavy swell from SE. by E., light winds; 6 p. m., a drizzling 

 rain, but Avith all these clouds and dampness we find the state of the barometer 

 as shown in the diagram, the lowest stand being 30.1 ; in the diagram statino- 

 the position of the ship and centre l:»earings, the storm disk with its hourly chang- 

 ing tangent angles is named a moderate gale ; the outside circle of a hurricane, 

 accompanied with a surrounding atmosphere slightly disturbed ; the greatest signs 

 of an approaching cyclone are the oscillations in barometer and sympiesometer, 

 more especially a high barometer with gloomy threatening weather ; in the track 

 of the trades and monsoons this is almost always a sure sign of a^n approaching 

 tempest. 



Looking at the table we must naturally be surprised to see that, regardless of 

 all these signs, the vessel was still kept on her course,, that is to say between 

 E.NE. and KE. by E. The question naturally arises, can the btirometer assist us 

 in forming an approximative estimation of the ship's distance from the centre? 

 And on first consideration, it is evident that there are very great differences in 

 the fall and rise of a barometer and sympiesometer, in various storms, thouo-b 

 they may be all true cyclones. Consequently the variations of these instruments 

 may ver}' often mislead us ; but the shortness of the time in which these changes 

 happened, the number of barometers Avhich underwent the same changes, was 

 enough to make even the most careless seaman comprehend the danger and the 

 close approximation of the destructive centre. But looking again at the barom- 

 eter and sympiesometer stand of January 5th, we find that it ought to have been 

 considered, first, the previous height of the barometer; second, the exact time for 

 a given fall or rise; and third, the change of the observer's position, especially 

 when running or steaming. The diagram here then shows the height and the 

 hourly change of a barometer and sympiesometer, and the distance from the 

 centre is worked out according to Mr. Piddington's rule. Certainly these calcula- 

 tions are only to be made approximatively, but coming so near to the truth that 

 we may consider the result to be the true centre. Now, as in the Southern 

 Indian ocean, the rate of travelling of a hurricane may be stated to be little 

 more than nine or ten miles per hour, and especially in the meridian between 

 Mauritius and Madagascar, the rate general!}' does not exceed eight miles per 

 hour, it is evident that with even the little progress the Monocacy made against 

 a head wind and sea, the course to the nortliward and eastward l)rought her 

 without question nearer to the focus. The weather during the following days 

 showed no material alteration; the same dark cloudy sky, the same height of 

 barometer, slightly varying as by the ship's progress we neared the centre. 

 The table shows the indications of barometer and sympiesometer for the 6th, 

 7th, and 8th, in her log-book. I find the oscillations of one barometer and the 

 vibrations of an aneroid barometer very strongly marked; both are common 

 signs dining a cyclone. On January 7th, states the log, the water changed its 

 appearance to a dark brown color, the sea was running furiously, and in various 

 directions ; the vessel was at that time under storm mainsail, double-reefed fore 

 trysail, and stonn fore topsail, the topsail yard and fore yard on deck, and fore 

 and main topmasts housed; everything was secured about her decks, and the 

 vessel kept under just enough steam to hold her own, but still heading to the 

 northward and eastward. During the night from the 7ih to the 8th the stonn 

 had reached its climax ; it blew the stonn staysail out of the bolt ropes, and the 



