8 COMPOSITION OF THE ATMOSPHERE 
become relatively more abundant with increasing 
height. 
The most direct method of finding the level where 
diffusive separation begins is the chemical analysis of 
air samples taken at great heights, smce the gravita- 
tional equilibrium should cause the O2 content to de- 
crease by 2 per cent per kilometre and the He content 
to merease by 14 per cent per kilometre. Air samples 
from the stratosphere have been obtained by manned 
and unmanned balloon flights. The results of these 
analyses are shown in Table VII. 
Taste VII. Composition or AIR IN THE STRATOSPHERE 
igh i variation Ox mn variati » 
ey eee: Meats a sat ay on Source of data’ 
9-17 0 G 
14.5 —0.14 d 
16.5 +0.5 + 0.5 e 
18.0 +0.35 + 0.1 é 
18.5 +0.7 + 0.3 0 €,a 
18.5 —0.38 d 
19.0 +0.55 + 0.15 —0.24 e,d 
21.0 +6.9 + 0.7 e 
21.5 —0.24 b 
22.0 +4.1 + 0.2 G 
22.0 +1.95 + 0.15 é 
22.5 +5.1 + 0.6 G 
22.5 +1.9 + 0:3 G 
23.5 +4.0 + 0.3 e 
23.5 +0.3 + 0.15 e 
24 —0.86 d 
25 2,1 = 023 e 
28-29 —2.5 d 
* Manned balloon flights Unmanned balloon flights 
(a) Prokofiev, 1933 (c) Lepape and Colange, 1935 
(6) Explorer IT, 1936 (d) EH. Regener, 1936 
(e) Glueckauf and Paneth, 1946 
It appears from this table that there is no significant 
change in either the He content or the O2 content below 
20 km. The He surplus observed between 21 and 25 
km averages 3.3 per cent, an enrichment which should 
be found at the top of a column of still air only 250 m 
high. The biggest O2 deficit, at about 28 km, corre- 
sponds to a column of still air only 1100 m high. It is 
therefore apparent that at the heights reached by 
sounding balloons there is sufficient turbulence to reduce 
the changes in the He content to about 149 of what 
one would expect from a gravitational equilibrium start- 
ing at the tropopause. The recent analysis by Chackett, 
Paneth, and Wilson [6] of three air samples collected 
by a V-2 rocket from a height of 50 to 70 km, gave 
variations of +0.3 to —4 per cent for He, variations of 
—0.3 to —0.7 per cent for Ne, and variations of —0.4 
to +1.0 per cent for A. These results make it certain 
that no diffusive separation is maintained even at these 
great heights. 
ISOTOPIC COMPOSITION OF THE 
ATMOSPHERIC GASES 
Increased attention to the isotopic composition of 
the atmospheric gases is likely to throw light on a 
number of problems. The composition in most cases is 
very similar to that found in the same atomic species 
in other parts of the earth’s crust* (see Table VIII). 
Water Vapour. Because of differences in the vapour 
pressures, mainly of 1H2O, 1H."O, and 1H°H**0, the 
density of atmospheric water should be slightly less 
than that in the oceans from which it originates. This 
was confirmed by Riesenfeld and Chang [19] who found 
a deficit of 3.8 y m the density of snow water, and of 
2.5 y for rain water (1 y = 10-*g ml). These figures 
are approximately what would be expected from the 
known vapour pressures. 
Oxygen. The differences in the composition of the 
oxygen in (liquid) water, gaseous oxygen, and carbon 
dioxide are much smaller, the densities being in the 
ratio 1:1.0000073:1.0000116 [23]. From this follows a 
slight enrichment of the 0 isotope in the ratio 
1:1.0033:1.0053. The difference of the oxygen density 
TasxeE VIII. Isoroprc Composition or THE Main 
ATMOSPHERIC GASES 
ic m: i es) and 
Element Atomic mass ine es percentages 
Hin HO (1) 99.98 (2) 0.02 
He (3) 1.1X 104 (4) 100 
C in COz (12) 98.9 (13) 2.1 (14) 0.95 X 10-42 
(14) 99.62 (15) 0.88 
O (16) 99.757 (17) 0.089 (18) 0.204 
Ne (20) 90.00 (21) 0827, (22) 9873 
A (86) 0.307 (88) 0.061 (40) 99.632 
for atmospheric CO: and for that of carbonate rocks 
is negligible [9]. 
Hydrogen. The difference in the isotopic composition 
between atmospheric H» and water vapour in air has 
not been determined, but if the two are in equilibrium 
(which is not necessarily the case), one would expect 
a considerably reduced deuterium-hydrogen ratio in the 
(D/A) water vapour __ 
(Ecce 3.6 (Suess [21]). 
Helium.® Much greater differences are observed for 
the *He content of helium found in air, in rocks, and 
in oil wells (Aldrich and Nier [2], and Coon [8]), the 
ratios *He/*He beg 1.2 X 107°, 1.5 X 10-7, and 
3 X 10-8, respectively. This clearly points to a differ- 
ent mode of origin of the two He species in the three 
cases. The *He in the atmosphere is suspected to arise 
from the reaction of nitrogen with neutrons derived 
from cosmic radiation. The *He in the lithosphere is 
presumably due to the action of neutrons on Lz where 
the neutrons arise from known reactions of small atomic 
nuclei with the a particles of the natural radio-ele- 
gaseous hydrogen, as 
4. The questions of the origin and development of the at- 
mosphere, though of interest to meteorologists, cannot be 
adequately dealt with in this paper. Attention is drawn to 
detailed articles by Chamberlin, Brown, and Kuiper [15, 
Chaps. 8, 9, 12], and by Wildt [24] where further references 
may be found. 
5. (Added in press) See also the recent note by P. Harteck 
and V. Faultings on ‘“The *He-Problem of the Atmosphere.’’ 
Nature, 166:1109 (1950). 
