210 



THE AGRICULTUEAL NEWS. 



July 10, 1909. 



The rate at which the storm travels along the 

 storm track (the translation) is not very great, ranging 

 from about 10 to 17 miles an hour in these lower lati- 

 tudes, but the velocity of the wind (in rotation) often 

 becomes very great. It is not known what the limit of 

 this velocity may be ; but it has been recorded up to 

 120 miles an hour, with an air pressure of over 70 lb. 

 per square inch. At the centre of the storm there is an 

 upward rush of air, which produces the effect of a calm 

 in the midst of the storm. 



Reference to the accompanying diagram will help 

 to make clear what has already been said about the 

 rotating movement of the wind and the forward 

 progression of the storm, the larger arrows indicating 

 the latter. The small letters accompanying the small 

 arrows indicate the direction from which the wind is 

 blowing with reference to the storm centre. 



The following premonitory indications are largely 

 taken from the United States' Pilot Chart. Before a 

 hurricane the barometer is somewhat higher than usual, 

 with cool, very clear, pleasant weather ; there is a long 

 low swell from the direction of the distant storni ; the 

 sky is covered with a quantity of light feathery cirrus 

 clouds (mare's tails) radiating from a point on the 

 horizon, where a whitish arc indicates the bearing of 

 the centre. If the cirrus plumes are faint ;uid opales- 

 cent in tint, fading gradually behind a slowly thicken- 

 ing haze or veil, the approaching storm is an old one, 

 of large area. If of snowy whiteness, projected against 

 a clear blue sky, it is a young cyclone of small area, but 

 great intensity. Great activity of movement of the 

 upper clouds while the storm is still distant indicates 

 that the hurricane is of great violence. 



As the storm approaches, the following unmistak- 

 able signs displcxy themselves: the barometer falls 

 rapidly: halos are seen arouiul the sun and moon: the 

 ocean swell increases : the weather becomes hot, moist 

 and oppressive, with litjlit variable winds: deep-red and 

 violet tints appear at dawn and sunset, tints which 

 assume a coppery glare of ominous aspect: a heavy 

 mountainous cloudbank on the distant horizon indicates 

 the position of the approa6hing storm : the barometer 

 falls more rapidly, and, finally, if the observations are 

 made on or near the storm track in the West Indies, 

 the wind begins to blow in a direction between the 

 north-east and north-west, soon rising to hurricane 

 force, increasing till the central calm passes, then 

 breaking out with violence from the south to south- 

 east. 



In the diagram, the northern portion of the storm 



is marked the dangerous semi-circle, because in this 

 semi-circle the wind all the time is from an easterly 

 direction, and all such winds blow to the front of the 

 storm. The southern, half of the storm is considered 

 the navigable semi-circle, because the wind in this 

 portion of the storn) is always from a westerly quarter, 

 and blows toward the rear of the storm. It may be 

 added that, owing to the usual track of these storms in 

 these latitudes being about south-east to north- 

 west, it follows that as soon as the word south 

 can be used in describing the direction of the wind, 

 the centre of the storm may be known to have passed, 

 and the worst may be considered to be over. 



IN HIGH LATITUDCS: 



Velocity alon^ track 



-.v^' 



c^t 



C.H,C J-_ 



20 to. 30 tuiLes per hour > ^^ ** ^/a/f* -^ ^" 



•r ^ 



e -J 



V v.- 



N,N.V«\ \ V . ' 1 



IN'MIDDLE LATITUDES ; 

 STORM RCCURViNG; 



Velocity- along tracli 

 5 to 10 milpB per iio'.^. 



tile, follcrwing latitTidi'tf ■ 

 June and Oct.. Int. 20' to 23= N 

 Jiily aiidSept,, Lat. 27'to29'K^ 

 August. lat 30' to 33" N. 



IN LO\N LATITUDES 



" Yelocity- along traci. 



Ubout n miJee per hour, (, n^«\ . I l^ 



It is useful for an observer on land to have a clear 

 understanding of the manner of ascertaining the 

 progress of the storm along its track from observations 

 on the direction in which the wind blows, and the 

 changes which the direction undergoes. 



It is clear from what has been said, that if the 

 observer faces the direction from which the wind is 



