184 Scientific Proceedings, Royal Dublin Society. 
As additional evidence, he gives the amounts of carbonic anhy - 
dride he found in air taken at the surface of the ground during 
September, 1877. The mean quantities for thirty day, and the 
same number of night, determinations were 6:41 and 7:00 respec- 
tively—thus showing the very considerable variation of 0°59 which 
could scarcely be due to anything else than ground air, as his 
experiments were made within the town of Buda Pesth, and pre- 
sumably the air was collected above a surface on which no grass 
was growing. 
Whether we take the view that the variations are caused by 
vegetation or by ground air, the seasons should have an influence, 
and according to v. Fodor this is actually the case. He gives 
figures from which the following mean variations have been 
deduced— 
EXCESS :— 
At Night. During the Day 
March, 3 k 4 — ‘ : 3 0:12 
April, : : é — : . : 0°39 
September, . : : 0°72 : 3 : — 
October, : 2 : 0°18 
November, - 3 : —— : 5 ‘ 0:02 
His explanation of these is as follows :— That the nightly carbonic 
anhydride is so high in autumn, while in spring more of the gas 
is found during the day, depends upon the fact that it is in autumn 
especially that the nights are cool, and consequently it is then that 
the atmosphere can most readily drive out the warm ground air. 
In the early part of the year, on the contrary, very little ground 
air streams out, and indeed at this time the atmosphere will gain 
carbonic anhydride from the soil by day rather than by night, for 
it is during the day time that the superficial layers of the soil get 
warmed through, and processes of decay are active. Some ob- 
servers have maintained that variations also occur during the day 
time, and among them were Méne and Truchot. Their figures, 
however, we agree with v. Fodor in thinking, are quite unreliable, 
and therefore we do not give them. 
As we have mentioned elsewhere, Fittbogen and Hiasselbarth 
found in the summer a sudden decrease shortly after sunrise, and 
a general decrease from then until mid-day, which they attribute 
to the action of the awakened and refreshed vegetation. 
