Vol, XVII. No. 42:.. 



THE AGKICULTUEAL NEWS 



247 



the heat necessary for their prolonged existence; and it seetcs 

 probable that the supply is insufficient until the mouth of 

 August, when the region of equatorial heavy rains between 

 South America and Africa reaches as far north as latitude 

 16'. It may be stated, however, that this theory of the 

 Jiiet?bani.>^ui of hurricanes is still under discussion by meteor- 

 clog is b". 



Ill considering hurricanes it i.s necessiry to distinguish 

 clearly between the two distinct movements of the storm, 

 which are known as rotation and translation. The rotation 

 of the storm is the nioveraent of the currents of air around 

 the centre, and the translation is the forward progression of 

 the whole storm along the storm track. 



The rate at which the storm travels along the storm 

 track (the translation) is not very great, ranging from about 

 10 to 1 7 miles an hour in these lower latitudes, but the velo- 

 city 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 ft 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 on the sea 

 from the direction of the distant storm; 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 iire 

 faint and opalescent in tint, fading gradually behind a slowly 

 thickening 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 j'oung 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 uninistakible 

 signs display themselves: the barometer falls rapidly; halos 

 are seen around the sun and moon; the ocean swell increases; 

 the weather becomes hot, moist, and oppressive, with light 

 variable winds; deep red and violet tints appear at dawn and 

 sunset, tints which assume a coppery glare or ominous aspect; 

 a heavy mountainous cloud-bank on the distant horizon indi- 

 cates the position of the approaching 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 

 iiorth-we.st, soon rising to hurricane force, increasing till the 

 central calm passes, then breaking out with violence from the 

 south-west to south east. 



In the diagram, the northern portion of the storm is 

 marked the dangerous semi-circle, because in this semi-circ!o 

 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 semicircle, 

 becau.se the wind in this portion of the storm is always from 

 a westerly-quarter, and blows toward the reir of the storm. 

 Ic nny be added tha*-, owing to the usual track of thes'.- 

 storms in these latitudes being about south-east to north- 



west. It follows that as soon aa 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 consid- 

 ered to be over. 



IN M(GH lATITUDCS. 



20 -f;\ 30 aulas per hour 



<^ 

 <, HN.t/ 



.^•s.t«* 



^ \ 3 



• M'MIDOLC LATITUDES, 

 STORM RECURVING: 



Velocitjr&IonJ trac^ 

 6 CO 10 iQilr.a psr hrac 



KOTB._Ear7-!cr,aas rpciirTo aiout ( 



I Uti . , -- 



' I Ulo foUcnring lalitti dija . 



I June and Oct.. Ut. 20' to 23-'N • 



'/ J"\5"aaidSept:, lat. 27"to29'iT '! 

 ', |» August. la.t 00' to 33" N. 



O.AiVc~ 



Ht/ 



IN tow LAT»TUDCjS 



5 Velocity- (lioag tmei. 

 "ikhout 17 milts pti hour 



% "~- :^ ./ / '• 



'% •"" fifm ^»"'* ■ 



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 chmges which the direction 

 undergoes. 



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

 faces the direction from which the wind is blowing, the 

 centre of the storm lies on his right hand. If he is directly 

 on the storm track, the wind will remain constant in direc- 

 tion, with increasing violence and a rapidly falling barometer 

 until the centre arrives; then there will be a short period of 

 calm, after which the wind will suddenly begin to blow from 

 the direction opposite to that previou.sly experienced, and 

 the violence will slowly abate as the centre passes away. 

 It is essential to be on the lookout for this occurrence of 

 wind of great violence after the passing of the central 

 calm. 



If the centre of the storm passes on the north side of 

 the observer, the wind will steadily shift from north to 

 north-west to west, and die away somewhere in the neigh- 

 bourhood of south-west. 



If, on the other hand, the centre p;isse3 on the s )uth, 

 the wind will steadily shift from north-north-east to e-ast 

 and die away some where in the south-east, 



