Climate of United States. 139 
notably the case in May, 1881. All the year through there is a permanent 
low pressure at the mouth of the St. Lawrence, due, in part, to the passage 
of storms, and, in part, to the permanent low-pressure area over Iceland, or 
the North Atlantic. 
Winds. The distribution of the winds is in accordance with that of pressure 
just given, that is, out of high areas, and around them clock-wise, and into low 
areas, and around them counter-clockwise. For example, from March to Oc- 
tober, the winds are emphatically from the high area in the Pacific, and this 
explains in part, if not entirely, the lack of rain during these months, for the 
cool, damp wind of the ocean, has its relative humidity diminished by the heat 
of the land. The general direction of the wind east of the Rockies, and north 
of 30° N., is from the west, with the exception that in the lower Mississippi 
Valley and Texas they are quite constant from the south. Distinctive trade 
winds are found south of 25° only and these are modified by the permanent 
high area in the south Atlantic. It may be said, that the upper current is 
constant from the west over the whole country all the months of the year, 
excepting a slight tendency in the warmer months for the upper current to 
coincide with the lower in the tradewind region. The wind on Pikes Peak, 
latitude 38° 50’ (14,147 feet), averages N. 82° W. a very little south of that 
in the warm months and north in the opposite season. On Mount Washing- 
ton, latitude 44° 16’ (6,300 feet) near the Atlantic, the wind is from N. 57° W., 
steady all the months; N. 48° W. in April and N. 62° W. in June being the 
extremes. 
Temperature. The lowest mean January temperature is — 5° F, 
(— 20.5° C.) in the northern portions of North Dakota and Minnesota. This 
makes a gradient of ı° F. (0.55° C.) per 25 miles from the Gulf to the extreme 
northern border, the former temperature being 55° F. (12.8°C.). On the 
Pacific coast the temperatures are 37° (2.7° C.) to 53° (11.6° C.) from the north 
to the south, a gradient of ı° F. in 70 miles. On the Atlantic coast, the range 
is from 20° F. (— 6.6° C.) to 65° F. (18.3° C.), a gradient of ı° F. in 30 miles. 
The highest mean January temperature is 71° F. (21.6°C.) at Key West. In 
July, the lowest temperature (56° F. 13.3°C.) is found at Eureka and 
Tatoosh islands, on the Pacific coast. A temperature of 68° F. (20°C.) at 
San Diego, California, rises to 92° F. (33.3° C.) at Yuma (the highest in the 
country at any regular station.. The range in the central region is from 66° F. 
(18.8° C.) to 84° F. (28.8°C.) or a gradient of ı°F. in 85 miles. On the At- 
lantic coast, the range is from 60° F. (15.5° C.) to 82° F. (27.7°C.) or ı°F. 
in 57 miles. 
Range of mean temperature from January to July. The greatest range 
(72° F.) is found in extreme North Dakota, and the least (8° F.) at Eureka, 
California. San Francisco has 9° F., Key West 14° F., New York City 43° F., 
Chicago 48° F. The difference between the normal minimum and normal maxi- 
mum temperatures will also give an idea of changes of climate, There is only 
7° F. at Tatoosh in January, ı0°F. at San Francisco, g°F. at Key West, 
