132 : Part II. Chapter 2. 
has a mean annual relative humidity of 42.9 per cent. in June. Santa Fe, 
New Mexico, has a mean annual of 44.8 per cent., with a mean monthly 
minimum of 28.7 per cent. in June, Pueblo, Colorado, has a mean annual 
of 46.2 per cent., with a mean monthly minimum of 37.6 per cent. in April 
while Death Valley, California, has a mean relative humidity of 23 per cent. 
during five months (May—September) of the year 1891. The atmosphere is 
very dry, absolutely, over the continents of middle and higher latitudes in 
winter, on account of the severe cold which then prevails, but it is relatively 
very moist and near saturation. Under these conditions, the relative humi- 
dity does not decrease inland, there it actually increases. 
The greater relative dryness of the continental interiors naturally involves 
also a smaller amount of cloudiness, especially in summer. The maximum of 
cloudiness in the United States is found on the northwestern Pacific coast 
(65 per cent). The lake region has a mean annual cloudiness of 60 per cent, 
while the greater part of the middle and south Atlantic coast has a percent- 
age of 5o and over the Mississippi and Missouri valley the average cloudiness 
is between 45 and 5o per cent. The mean annual cloudiness in southern 
Nevada, southeastern New Mexico, most of Arizona is 30 per cent. — The 
amount and frequency of precipitation as a-rule decrease inland, but this 
decrease is so irregular and depends so much upon topography; upon the 
position of the mountain ranges with respect to the rain-bearing winds that 
no general statement can be made. 3 
The influence of continents upon winds is of the great climatic im- 
portance. Land and sea breezes are local phenomena limited to the sea- 
coasts. With the change from day to night, the relative temperature con- 
ditions of land and water are reversed followed by a reversal of the winds. 
In countries where there is no real winter, these periodic winds blow throughout 
the year. Thus on the south coast of southern California the sea breeze 
blows throughout the greater part of the year, weak in winter and strong in 
summer. In higher latitudes, they occur almost exclusively in the warmer 
months. Thus on the New Jersey coast of the United States, according to 
the observations of the writer, the sea breeze begins first over the open ocean, 
as shown by the sails of ships and the smoke of steamers and gradually 
works in toward the coast, which it reaches on very warm quiet mornings at 
about g o’clock. Frequently, however, the arrival of the sea breeze is delayed 
until eleven o’clock, or noon. On several days during one summer, the tem. 
perature in the early morning stood at go°F. (32.2°C.), but with the arrrival 
of the sea breeze, a drop of from 10—ı5 degrees F. was recorded with i 
a period of a little over ten minutes. Lake breezes are also of frequent 0C- 
curence. An excellent example is described by HazEn’). During the summ 
of 1882, observations were made at the lake crib, a water-tower station, thr 
ı) HAzEn, H. A.: Report on wind Velocities at the Lake Crib and at Chicago. United States 
Signal Services Notes; No. VI. 1883. 
