THE COMPOSITION OF ATMOSPHERIC ATR 9 
ments. The connection of *He in minerals with Lz is 
borne out by the abnormally high *He/*He ratio in 
spodumene, a lithium aluminium silicate. 
Carbon. Another isotope which owes its existence to 
the neutrons from cosmic radiation is the radioactive 
140, which is produced by “N + n — 1H + MC. 
As cosmic ray neutrons are produced mainly in the 
upper atmosphere, the “C starts its career as CO, and 
enters into all organic matter by the process of plant 
assimilation. After the death of the plant the radio- 
active carbon decays with a half-life of 5720 years, so 
that old coal and oil deposits are no longer radioactive. 
The proportion of radiocarbon was found to be 0.95 
x 10- g of “C per g YC in living matter [3]. 
FUTURE DEVELOPMENTS 
Oxygen and Carbon Dioxide. Our best values of the 
O2 content or, for that matter, of the O. and CO; 
content of air date from 1912. Since then a number of 
improvements in the control of thermostats and in all 
manner of measuring devices have been made, which 
should render possible an increased accuracy. A re- 
determination is particularly desirable in order to get 
an idea of any long-term variations of the O2 content 
of air. 
There are, moreover, the unexplained O2 values of 
Lockhart and Court in the Antarctic which should be 
either confirmed or refuted. This applies also to the 
high CO, values observed by Krogh in certain arctic 
regions, where the observed variations were very large, 
and further investigations are likely to bring to light 
some interesting phenomena responsible for such 
changes. Callendar’s suggestion of a CO increase during 
this century due to industrial CO2 production requires 
that the CO; content of the Northern Hemisphere should 
be slightly larger than that of the Southern Hemi- 
sphere, a feature which should be subject to experimen- 
tal verification by modern techniques. 
The results of Buch and of Wattenberg make it 
fairly certain that there is a CO: circulation in the oceans 
involving uptake of CO. at high latitudes and its re- 
lease at low latitudes. Some light on the time scale of 
this cycle might be thrown by a “C analysis of the 
CO, released from the sea at low latitudes, which, if 
the cycle exceeds 10? years, would result in a noticeable 
decrease of “C activity. 
Methane. The CH, in the atmosphere, discovered 
only recently, still offers a few problems. Its percentage 
iM air requires more accurate determination, and the 
question of its production requires further study. 
Hydrogen. Our knowledge of the H» content of the 
air is so far inadequate. 
Ozone. Large gaps still exist in our knowledge of the 
atmospheric O; near the ground. Its geographical dis- 
tribution at ground level is quite unexplored; its de- 
pendence on weather conditions has only been touched 
on, and requires much more systematic investigation, 
particularly with reference to its vertical distribution. 
The increased occurrence of 03 near cloud levels and 
its connection with thunder clouds also require more 
detailed investigation, including a study of its possible 
mode of generation under such conditions. 
Upper Atmosphere. It now seems certain that the 
upper atmosphere has essentially the same composition 
as that found at the ground, at least up to heights of 
70 km, though further confirmation of the rocket data 
is desirable and will no doubt be obtained in the near 
future. This uniformity means that turbulent mixing 
in the stratosphere is considerably greater than was 
formerly expected. An explanation for this turbulence 
has been suggested by Brewer [4] who assumes an air 
circulation involving a movement of air into the strato- 
sphere at the equator followed by slow poleward move- 
ment in the stratosphere, accompanied by a slow sinking 
movement in the temperate and polar regions. As this 
hypothesis requires the abandonment of the idea of a 
stratosphere which is in radiative equilibrium, many 
new and interesting problems arise which require ex- 
perimental confirmation. 
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