124 NOETH ATLANTIC WINDS AND WEATHEB. 



read 29-87, on the 19th 29-78, fall in the 24 hours 0-09. The barometrio 

 differenoe between the stations on the 18th was -14, on the 19 bh -16. If, 

 then, the barometer at the ship, on the 18th, off Dover, read 29-87, and 

 off Portsmouth on the 19th, 24 hours afterwards, 29-94, the captain would 

 record a rise of 0-07, the barometer having really fallen 0-08 at a point 

 intermediate between the stations: thus, while a real gradient of + -142 

 existed between Dover and Portsmouth on the 19th, the barometer having 

 fallen at both stations during tJie previous 24 hours, a captain sailing from 

 Dover to Portsmouth during the same 24 hours would record an apparent 

 gradient of + -062, the reduction from the real gradient arising from the 

 fall of the barometer at both stations, while the rise of his barometer 

 resulted from his sailing toward the region of higher pressure."* 



3.-N0RTK ATLANTIC WINDS AND WEATHER. 



(42.) The Wind Begions of the North Atlantic Ocean may be thus 

 defined : — To the North of the Tropic of Cancer are the Anti-Trades,] or 

 Passage Winds, which, though variable, have a general tendency from 

 S.W. to N.E. ; in these temperate and Arctic regions the general barometric 

 pressure is moderate, with occasional appearances of areas of high pressure. 

 South of these is a belt of Calms and Variable Winds, distinguished by a 

 high barometer, called by Commander Maury the "Calms of Cancer," also 

 known to sailors as the "Horse Latitudes," as hereafter explained. This 

 belt varies between 30° and 35° N., according to the season. South of 

 this, and extending to about 8° to 5° N., but varying in its Southern as in 

 its Northern limits, is the great region of the N.E. Trades. In the space 

 between the Equator and this region of Trades are the " Doldrums," or 

 Calms, of the Equator; and upon the African coast there is a regular 

 alternation of the winds, similar to the monsoons in other parts. Each of 

 these regions will be treated of separately in the following pages. 



(43.) In the spaces which separate these wind systems those storms 

 known as Hurricanes, Tornados, Typhoons, or Cyclones occur. This 

 important branch of the present subject is fully considered hereafter, but 

 the occurrence of storms is an exceptional case in the vast system of 

 atmospheric circulation we have been considering. 



♦ Those wishing further information on this subject should refer to a Paper on 

 " Barometric Gradients in connection with Wind Velocity and Direction at the Kew 

 Observatory," by G. M. Whipple and T. W. Baker, in the Quarterly Journal of the 

 Meteorological Society, 1882, pp. 198—203. 



t The term " Anti-Trades," adopted by Sir John Herschel, is expressive and appro- 

 priate. By others they have been named Counter-Trades, which designation may more 

 exactly define the upper currents over the Trade Winds. They have also been vaguely 

 caUed " The Variables," a term which is best confined to the characteristic of the Belts 

 of Calm or shifting winds about the Tropics. 



