90 THYSICAL GEOaEAPHY OF THE SEA, AZW ITS MSTEOr.OLOGY. 



or the soutli-west comer of Texas bordering tlie G-iilf of Mexico, lat. 

 27^.5. They are often felt to the west in Mexico, but rarely in 

 eastern or northern Texas. The fact that they are not kno'vvn in 

 northern Texas goes to show that the cold they bring is not- 

 translated by the smiace winds from the north. 



243. A correspondent in Nueces, lat. 27^ 36' N.y long. 97^ 27' 

 Their severe cold. ^,Y.^ bas described thoso winds there during the- 



winter of 1859-60 : They prevail from November to March, and 

 commence with the thermometer at about 80^ or 85°. A calm 

 ensues on the coast : black clouds roll up fi'om the north ; the 

 wind is heard seyenil minutes before it is felt ; the thermometer 

 begins to fall ; the cold norther bm^sts upon the people, bringing 

 the temperatm'e down to 28^, and sometimes even to 25°, before the 

 inhabitants have time to change clothing and make fires. So severe 

 is the cold, so dry the air, that men and cattle have been known to 

 perish in them.* These are the ■winds which, entering the Gulf 

 and sucking up heat and moistm-e therefrom, still retain enough 

 of strength to make themselves terrible to mariners — they are the 

 far-famed northers of Vera Cruz. 



244. The temperatm^e of the atmosphere at the height of three or 

 "Cold Snaps." four milcs is Variable — observations and balloonists 



tell us so. Air may be brought below the normal temperatm-e 

 due the height at which it may be, by radiation and other 

 processes. It may also be raised above that normal temperature 

 hj the setting free there of the latent heat of vapour, or by the 

 action of the solar ray upon the cloud stratum. When this upper 

 air is brought to the surface in this abnormal condition, the people 

 of the district upon which it descends find themselves in a " cold 

 snap " or "hot term," as the case may be. 



245. That our climates, especially the continental, are affected 

 j\nemorrieters to de- by, and that many of the changes in the weather 

 Sn'oTthe wS^d "'^" arc due to, the vertical circulation of the atmosphere 

 '^'^°^'^'^- seems clear.! We have other evidence besides that 

 of induction (§ 224) as to upward and do^vnward movements 



* " Two men," says T.Ir. M. A. Taylor, in a letter dated January 11th, 1S69, at 

 Nueces, Texas, " were actually frozen to death within a few miles of this place 

 this winter in a norther. Animals seem to tell by instinct Avhen the norther is 

 coming, and make tlieir way from the open prairies to timber and other shelter, 

 startin'j; often on a run when the heat is not oppressive. Tiiis is when the change 

 is to bo su<lden and violent. Many cattle, horses, and sheep are frozen to death 

 at such times." 



t Vide Chapter XXI. 



