METEOROLOGY OF I 8q7 
51 
line, is 35 miles, and the difference in elevation is 4,000 fr. 
The higher station has an average temperature for the 
year over g° colder than Fort Collins. In the summer, 
from May to September inclusive, the mountain station 
averages 13° colder, while during the winter months of 
January, February and March, it averaged but 6° colder. 
It was, therefore, relatively warmer during the winter than 
during the summer. ^ 
§51 If the records are compared day by day, it is 
noticeable that the temperature at the higher station is 
often higher than at Fort Collins during the winter months, 
and this notwithstanding 4,oog feet difference of elevation. 
When first noticed some years ago, some doubt was felt 
as to the reality of the phenomena. Continued observa- 
tion has not only confirmed it, but shown that in the winter 
months from December to April, it is very common. In 
some years the average temperature at the higher st^ation 
has actually been above that at Fort Collins during the 
winter months. Such inversions of temperature have been 
observed between Denver and the summit of Pikes Peak. 
§52 Many of the differences are due to the fact that 
the cold waves which sometime reach us in the winter from 
the north, consist of a wave of cold air, relatively shallow, 
which underruns the layer of warmer air, displacing it, 
and the cold wave is not in itself deep enough to reach up 
to the mountain stations and submerge them in its wintry 
bath. When the cold is due to local radiation, as when the 
ground is covered by a thin layer of snow, then the temper- 
ature at the mountain stations descends lower than on the 
1 Fiins. 
