Lerrs & Buake—TZhe Carbonic Anhydride of the Atmosphere. 197 
Further, he compared fifty-three days on which rain fell after 
dry weather with three day spells immediately after each, with the 
following results :— 
Mean vol. COz in 10,000 of air— 
Rainy days. 3-day spells after rain. 
Winter [ Nov.—April], : 3°78 3°68 
Summer [May-October], . 3°68 3°90 
and concluded that the lowering effect on the carbonic anhydride 
observed after rain is lasting in winter, but that in summer there 
follows a considerable increase after such diminution. Petermann 
and Graftiau give the following figures for Gembloux :— 
General mean [525 observations], _ . ; 2:94 
Rainy weather [120 2 Hales : 2°93 
and do not consider that rain has any perceptible influence. 
As regards the nature of the effects produced by rain, it has. 
been suggested that it may itself act as absorbent of atmospheric: 
carbonic anhydride (which is improbable, in view of the fact that 
by the law of partial pressures 1 litre of distilled water should 
dissolve only about 0:8 c.c.), or that it may induce changes in the 
soil causing either evolution or absorption. 
v. Fodor, Wollny, and others who consider that ground air 
plays the chief réle in the variations of atmospheric carbonic 
anhydride, lay stress on the latter explanation, 7c. the influence of 
the rain on the soil and ground air. Thus warmth and moisture 
will promote decomposition of the organic matter of the soil, and 
consequently augment the amount of carbonic anhydride in the 
ground air, and eventually that of the external air also, whence. 
the increase noticed by v. Fodor in the air after rainy weather in 
summer. On the other hand, in winter, where putrefactive changes 
are not active, absorption of carbonic anhydride by the wet soil 
will occur without any overbalancing evolution and hence the 
explanation of y. Fodor’s results concerning the air after rain in 
winter.’ 
As regards snow, there seems to be an agreement among the 
observers that atmospheric carbonic anhydride is in excess when 
it is falling. 
1 See p. 215. 
