392 



Observations on the Physical Geography 



seven degrees of latitude, being as great nearly as between the 

 eastern and western borders of the Atlantic. 



Peculiarities of climate are to be traced to the prevalent winds, 

 the height and position of a country, and the courses and heights 

 of its mountains. The winds from an open ocean, as has been 

 often observed, will seldom be much colder than the temperature 

 of the ocean itself, and this is below freezing:. But winds from the 



7 C7 



land partake of the heat and cold of the land, which have a wide 

 range. Thus in Tierra del Fuego in latitudes 52° to 55°, the 

 temperature of winter is comparatively mild.* Again, when the 

 winds come from over open arid land in summer, as happens at 

 times in Eastern Australia, and often with all 

 cinity of deserts, there is an excessive heat in the atmosphere ; 

 or when they blow from northern territories covered with snows, 

 as is common in winter in the northern portion of the United 

 States, extreme cold is the necessary consequence. 



In Western America the prevalent winds are from the ocean. 

 This fact alone is a sufficient cause for the mildness of the 

 seasons, as compared with eastern America.f But besides this, 

 when a land breeze blows in the colder months, it comes usually 

 from the southward and eastward and seldom from the northward 

 or north-east ward. % 



The same facts explain the peculiar dryness of the climate in 

 summer, and the occurrence of rains in winter. The oceanic 



regions in the vi- 



* Fitzroy, who spent many months of different years about Tierra dd Fuego, 3 



that in June of 1834, (corresponding to our December,) the thermometer did Dot 

 sink below :i8^° F., and the mean of the first twelve days was 41° F. In Feb- 

 ruary of the same year, (corresponding to our An tst,) at Port, Famine, the ther- 

 mometer ranged between 47f^ and 5?4 U - la 1 <»ruary of 1838, at i <>d Sacoe 



Bay, and in that vicinity, (i; -. 53 to 55,) the thermometer ranged from 461° to 51 . 



f Capt, Wilkes observes on this point, "I am disposed to believe this (the heat 

 of summer) to be owing to the prevalence of southwesterly or ocean winds.'' — Nar- 

 rative, f, 139. 



% From the table by Mr. Ball, referred to on page 390, we obtain the following 

 facts, relating to the prevalent winds of the months of the year. 





| WVstPrlv. 



1 E * 



9 day 



• * 



S.E. 



S. 



■i 



N.E. and N. 



# • 



* • 



November, 1832, 

 December, . 



13 days. 

 5 



1 8 days. 

 24 



January, 1833, 



6 



18 



8 



1 



• • 



February, 



12 



1 



7 



5 



2 



March, 



25 



• t 



4 



2 



• * 



April, . 



22 



ff • 



3 



3 



4 * 



May, 



22 



• • 



4 



4 



• * 



June, ... 



24 



■ • 



• • 



1 



5 



July, 



21 



2 



• * 



• • 



6 



August, 



20 



1 



i 



• # 



4 



September, 



j 11 (varia 



i bles8dv 



• • 



2 



2 



4 



1 October, 



18 



5 ! 



9 



« 



2 



East winds were observed only three times* during the summer the Exploring 

 Expedition was in Oregon. The winds were almost constant from the W.N.W . to 

 W.S.W. 



