904 Eighteenth Memoir on the Law of Storms. [Sept. 



I have given in diagram No. III. the true projection of a section of 

 the following, or rear, half of a Cyclone of 150 miles in diameter, on the 

 line of its track, both horizontally and vertically, to a scale of 10 miles 

 to one inch, to shew the lifting up clearly ; in which the disk on that 

 side is shewn as having lifted itself two miles above the surface of the 

 ocean, and is thus giving to the ships involved in it 75 miles of its 

 fury in front, and but 50 miles in its rear portion ; or to express this 

 in Time ; it is a Cyclone which, if it was moving at the rate of 10 miles 

 per hour would last 7\ hours in its onset, till the calm reached, and 

 but 5 hours in its decline. If we take our diagram to represent the 

 following or rear half of a Cyclone of 300 miles in diameter, or double 

 its scale,* as marked on the second line of figures below, we can under- 

 stand at once how the lifting up of the following part of the disk 

 would much diminish the extent and duration of the Cyclone to the 

 little ships marked upon the diagram, say to 10 hours of time, while 

 those in the advancing circles would have the whole extent of the semi- 

 Cyclone in that direction passing over them, which would require 15 

 hours. 



Cyclone seen through, at its centre. 



As connected with its extent we may remark here also upon its 

 height, or more properly thickness, which appears to have been very 

 insignificant, perhaps not more than a mile or two, for it will be 

 observed that while the JEdmundsbury had it at the calm centre " much 

 lighter overhead," Mr. Brackly at the False Point Light House had 

 " the rain clearing off and saw the stars very clear overhead, but a thick 

 bank of haze all round," so that it appears to have become thinner as 

 it approached the land ? The Camperdown also from 7h. to 7h. 30\ 

 p. m. in the calm had it "fine overhead." 



Hot and Cold blasts, Hail, fyc. during the Cyclone. 



Capt. Arrow of the Wellesley, it will be seen, noted this phseno- 

 menon of alternate hot and cold blasts, comparing the first to the 

 Scirocco. The Charles Kerr and Futtle Rozack also experienced, if not 

 hail, sleet. These indications are of some importance, inasmuch as hail 



* For the sake of the even numbers : We have 280 miles for the diameter of 

 our present Cyclone, as measured by the advancing circles on the 12th, and 230 on 

 the 13th. 



