Letrs & Buake—The Carbonic Anhydride of the Atmosphere. 185 
vy. Fodor has investigated this matter, and, as the result of 
numerous and careful determinations, came to the conclusion that 
the amount is fairly constant during the day, but experiences a 
considerable increase in the evening—the excess observed at night 
time being poured into the atmosphere from the ground, chiefly 
during the evening hours. 
Influence of Vegetation. 
It is somewhat remarkable that very few details are to be 
found in the numerous memoirs which we have studied which 
bear on this point. Truchot found a marked increase in the 
quantity of atmospheric carbonic anhydride in the neighbourhood 
of vegetation, varying during the day from 0°40 vols. per 10,000 
(sun) to 1:01 (cloud). 
Reiset’s results are somewhat conflicting. He tells us that 
the mean of 27 observations made of the air in a well-wooded 
coppice gave 2°917, while that obtained at the “field station ”’ 
(with samples taken at the same hours) amounted to 2-902, 
showing, therefore, a slight excess in the former. On the other 
hand, five samples taken over a field of red clover in full flower in 
June showed an appreciable diminution (mean = 0:017) from that 
taken at the “‘ normal station’’; and also that in a barley field 
planted with lucern in full vegetation a larger diminution (mean 
= 0104) was found. 
Mintz and Aubin, without making any special experiments 
on the influence of vegetation, explain the fact that atmospheric 
carbonic anhydride is at its minimum when the sky is clear and 
the air agitated, by the increased activity of vegetables, and the 
rapid diffusion (by wind) of the carbonic anhydride produced at 
the surface of the soil. 
Fittbogen and Hasselbarth found during observations made in 
the summer that a decrease was apparent from sunrise to mid-day, 
and all their experiments showed a sudden decrease shortly after 
sunrise, which they attribute to the action of the awakened and 
refreshed plants. 
Simultaneous observations made by Wollny in calm weather 
