CLIMATE OF MEXICO. 



51 



of the Gulf and the slopes of the mountaius. But their normal direction ig 

 frequently modified by the great inequalities of the relief and the trend of the 

 mountain ranges. The so-called nor les, or northern gales, which prevail especially 

 from October to March in the Gulf waters, and which are justly dreaded by 

 skippers bound for Tampico or Vera Cruz, are nothing more than the trade winds 

 deflected from their course, and attracted southwards by the heated and rarefied 

 atmosphere of the low-lying plains of Yucatan. United with the cold current 

 which sweeps down the Mississippi, the trades blow wàth tremendous fury along 

 the seaboard, the storms often lasting for several days, and even a whole week, 

 to the great danger of the shipping on these exposed and harbourless coasts. The 



Fig. 25. — ISOTHEEMALS OF MeXICO MODIFIED BY ALTITUDE. 

 Scale 1 : 30,000,000. 



West dp breenwich 



'«.*. 



to 50^ F. 50^ to 59° 



to 68° 68° to 77° 77° and upwards. 

 — _— _ 620 Miles. 



full force of the norte is scarcely felt on the plateaux, and its strength is completely 

 exhausted before it reaches the Pacific slope. 



The shores of this ocean have also their special atmosj)heric currents, which 

 are determined by the disposition of the coastline, and the form and elevation of 

 the neighbouring mountains. At irregular intervals during the summer the arid 

 and superheated plateaux attract the aerial masses from the equatorial waters, and 

 the Mexican uplands are at least once a year visited by sudden squalls sweeping 

 along the Columbian and Central Am^erican seaboard. At times they assume the 

 character of a veritable cyclone, blowing in a few hours from every point of the 

 compass. In 1839, one of these gales wrecked twelve vessels in the port of 

 Mazatlan ; and Manzanillo, the Port of Colima, was destroyed by another in 1881. 



