UTAH ACADEMY OF SCIENCES 57 
Observations taken on mountains side or tops are very 
different from observations taken in the free air. The 
atmosphere is cooler over mountain tops than in the free 
atmosphere at the same altitude. This is due probably 
to the fact that air cools as it rises, and as air is generally 
in motion, there is a current of air being constantly forced 
up the mountain side and over its top, which is cooled by ex- 
pansion and in addition by the free radiation from the 
mountain peak. 
For purposes of study the atmosphere may be divided 
into three portions: or layers: 
The first includes that portion extending from the 
earth to 3000 m. 
The second from the 3000 m. level to the 10000 m. 
level. 
The third all above the 10000 m. level. 
In the first layer, or all that below the 3000 m. level 
is a region of considerable atmospheric turmoil. Here 
the winds are irregular in direction and vary considerably 
in speed. It is the storm layer, although the vortical action 
of a cyclone or anticyclone extends into the next higher 
level. Here the temperature frequently, especially in sum- 
mer, rises with increase in altitude, and the temperature 
condition is controlled almost entirely by the passing of 
highs and lows over a place. 
The second layer, or that between the 3000 m. and 
10000 m. is a region of uniform temperature changes. This 
region is comparatively free from clouds, the temperatures 
fall with the adiabatic rate. There is an absence of atmos- 
pheric turmoil characteristic of the first layer. The vorti- 
cal action due to cyclones and anticyclone extends into this 
layer, but as a rule its normal condition is one of stability 
and usual freedom from clouds. 
The thin layer or that above the 10000 m. level is a 
region which is particularly interesting. Here the tem- 
perature gradient is positive—a fact which was unknown up 
to a short time ago. Occasional observations indicate an iso- 
thermal condition and for this reason it is called the iso- 
thermal layer. 
