UTAH ACADEMY OF SCIENCES 59 
in the isothermal region the conditions are reversed; here 
the air is being warmed by radiations from the moist air 
below when the barometer is low. But when the barometer 
is high, and the air relatively dry, it will conserve its own 
heat and allow the upper air in the region of the upper in- 
version to become cold. 
CAUSE OF THE UPPER INVERSION. 
There have been all kinds of explanations of the 
cause of this upper inversion. 
Mechanically we have divided the atmosphere into 
three parts or layers, the first of which is the region of 
terrestrial disturbance. The second, that lying between the 
3000 m. and the 10000 m. which is the region of uniform 
temperature changes; the third, that lying above the 10000 
m. level, or the region of the upper inversion. 
Spectroscopically we have three layers corresponding 
to these mechanical layers. The first the black body por- 
tion which comprises all below the 3000 m. level where 
most of the water vapor exists. Second, the diathermous 
or dry air above that containing most of the water 
vapor. Third, the selectively absorptive, or the air of the 
isothermal layer, presumably rich in ozone. 
Solar radiation ranging from 2.5 mu. down, the max- 
imum intensity between .4 mu. and .5 mu. Now what ex- 
tent of these radiations are absorbed by the atmosphere 
and the earth is not easy to say as it depends upon many 
things, the wave-length, kind of gas or substance, the 
amount of gas through which it passes, which is the same 
thing as saying its partial pressure, and even to the total 
pressure to which the gas is subjected, and to probably 
more. 
In the lower levels there are about 5 to 12 per cent of 
the energy absorbed, the remainder is either absorbed or 
reflected by the clouds, dust or the earth itself. That 
portion of the radiant energy which is simply reflected is 
returned with its wave length unchanged. That part which 
is absorbed has its wave-length changed into waves of great 
length relatively. Water vapor absorbs a large amount 
