1851.] On the Comparative action of Aneroid Barometers. 223 



Hence it will be seen that the Simpiesometer had about double the 

 fall in the first 12 hours on the approach of the Cyclone, and that the 

 entire fall of the instruments was, for 25J hours, or from the first fall 

 up to the passage of the centre, as follows : 



Mar. Bar. Aneroid. Simpiesometer. 



0.40 0.43 0.61 



The Simpiesometer giving one third more fall than the Marine 

 Barometer and Aneroid. Throughout this Cyclone the Thermometer 

 varied only 4°; being at 84° at 8 a. m. on the 26th, and at 80° from 

 1 A. m. to 6.20 a. m. on the 27th. The above table is projected on 

 the plate, which is drawn to a vertical scale of 2 inches for one. 



Cases of very severe Cyclones have occurred, especially in the 

 Southern Indian Ocean, in which the fall of the Barometer has been 

 so insignificant as wholly to mislead the seaman, but the Simpiesometer 

 has both shewn a greater depression and shewn this in time to put 

 him on his guard. Notable instances of this are the Cyclones of the 

 Buccleugh and of the Vellore ; the last investigated by Dr. Thorn. In 

 the Buccleugh' s Cyclone though of terrific violence (See Sailor's Horn 

 Book, p. 232, 2nd Edition) the Barometer did not fall below 29.76 on 

 its approach : but the Simpiesometer had been 0.38 lower for a week 

 previous, and fell 0.82 lower than the Barometer during the Cyclone. 



But it will be remarked of the Tavoy's tahle just given, that after the 

 depression of the first twelve hours, or say from a to b on the plate, and 

 on the rise after the greatest depression, the instruments shewed nearly 

 the same differences ; and I have said above that I was speaking 

 theoretically of the probable action of the Aneroid as regards time of 

 warning, which for the Mariner is the one thing needful. This I will 

 now endeavour to explain, and those who have considered the subject 

 of Barometers philosophically will agree I think with me that the result 

 here detailed goes far to justify one of the two theoretical objections 

 which the construction of the Aneroid suggests ; and which strange to 

 say, has never been adverted to by the inventor or sellers, that I am 

 aware of. And it is this. We are told a good deal of temperature, 

 but they seem to have taken no notice of another great principle in 

 physics, Inertia, and to this I attribute at once the superiority of 

 the Simpiesometer. 



