Lerts & Bhaxe—The Carbonic Anhydride of the Atmosphere. 217 
diagrams showing the average monthly variations of the above factors, 
which bear out most of his general conclusions. 
So far as ground air is concerned (Plate XVII.), it will be seen that 
the variations of its carbonic anhydride, both at higher and lower levels, 
correspond fairly closely with those of atmospheric temperature, and 
consequently with the seasons. It is also clearly seen that the amount 
at deeper level is always greatly in excess of that at higher level. 
The second series of curves (Plate XVIII.) is more complex; but 
certain points are clearly brought out. Thus the air at ground-level is 
shown to contain more carbonic anhydride than that at some distance 
above the ground during the warmer part of the year, but sinks below it 
in winter and early spring; also, as v. Fodor insists, the variations in 
carbonic anhydride at ground-level are much more considerable than 
those in the air above it. The effects of rain are clearly shown—the 
maxima of rainfall corresponding, as a rule, with minima of carbonic 
anhydride at ground-level, and, broadly speaking, the converse is also true. 
As to the effects of ground air on atmospheric carbonic anhydride, 
if we neglect the parts of the curves from November to April, when the 
soil appears to be acting as absorbent, we certainly find an increase 
both in the carbonic anhydride of the ground air as well as in that of 
the atmosphere from April to June; but from June to September the 
curves for these two slope in opposite directions. It is possible that 
the effects of rain, wind, and changes in pressure, may partly explain 
this, and also it is by no means inconceivable that outward streamings 
of ground air would lower the amount of its carbonic anhydride, while 
increasing that of the atmosphere close to the soil. 
As regards the probability of ground air influencing to any consi- 
derable extent the amount of atmospheric carbonic anhydride, the 
following considerations have occurred to us :— 
Imagine a tube, 100 square centimetres in sectional area, inserted 
through the soil and projecting into the air. Suppose that in the soil it 
became sealed by underground water, at a depth of 25 metres, and that 
it projected into the air to a height of 2 metres. It now contains 20 
litres of ordinary air above and 250 litres of soil below. Further, 
suppose that the porosity of the soil amounted to 20 per cent. of its 
bulk, then the tube would contain 50 litres of ground air. Let us 
assume that this ground air contains 1 per cent. by volume of 
carbonic anhydride. ! 
1From the monthly averages given by v. Fodor, the mean annual values for the 
carbonic anhydride in the soil, at depths of 1, 2, and 3 metres, are respectively 1:02, 
1°61, and 2°81 per cent. by volume. 
