90 THE PHYSICAL GEOGRAPHY OF THE SEA. 



several minntes before it is felt ; the thermometer begins to fall ; 

 the cold norther bursts upon the people, bringing the temperature 

 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 per- 

 ish in them.* These are the winds which, entering the Gulf and 

 sucking up heat and moisture therefrom, still retain enough of 

 strength to make themselves terrible to mariners — they are the 

 far-famed northers of Vera Cruz. 



244. We now see the general course of the " wind in his cir- 

 The wind in his cir- cuits," as wc scc the gcucral course of the water in 

 '^"'*^- a river. There are many abrading surfaces, irreg- 

 ularities, &c., which produce a thousand eddies in the main stream ; 

 yet, nevertheless, the general direction of the whole is not disturb- 

 ed nor affected by those counter currents ; so with the atmosphere 

 and the variable winds which we find here in this latitude. Have 

 I not, therefore, very good grounds for the opinion (§ 200) that 

 the " wind in his circuits," though apparently to us never so way- 

 ward, is as obedient to law and as subservient to order as were 

 the morning stars when first they " sang together?" 



245. There are at least two forces concerned in driving^ the 

 Forces which propel wiud through its circuits. We have seen (§ 207) 

 the wind. whcucc that forcc is derived which gives easting to 

 the winds as they approach the equator, and westing as they ap- 

 proach the poles ; and allusion, without explanation, has been 

 made (§ 212) to the source whence they derive their northing and 

 their southing. Philosophers formerly held that the trade-winds 

 are drawn toward the equator by the influence of the direct rays 

 of the sun upon the atmosphere there. They heated it, expanded 

 it, and produced rarefaction, thereby causing a rush of the wind 

 l)<:»th from the north and the south ; and as they played with 

 greatest effect at the equator, there the ascent of the air and the 

 meeting of the two winds would naturally be. Such was the 

 doctrine. 



* "Two men," says Mr. M. A. Taylor, in a letter dated January 11th, 1860, 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 when the norther is coming, 

 and make their way from the open prairies to timber and other shelter, starting oft- 

 en on a run when the heat is not oppressive. This is when the change is to be sud- 

 den and violent. Many cattle, horses, and sheep are frozen to death at such times." 



