202 Scientific Proceedings, Royal Dublin Society. 
the anti-cyclonic type of weather, and all observers agree that the 
carbonic anhydride of the atmosphere is then at its maximum. 
The effects which are likely to be produced by the cyclonic 
type of weather are perhaps even more difficult to forecast. In 
the centre of the system the air currents are ascenscional, and an 
inrush occurs along the adjacent surfaces. Hence the amount of 
carbonic anhydride present in the air, at a given spot on the latter, 
should depend upon the nature of the surface which the wind has 
previously traversed. If this happens to be water, less carbonic 
anhydride might be expected than with land, as the latter con- 
tains the chief sources of evolution, both natural and artificial. 
Theoretically, dimunition of pressure should lead to an increase of 
atmospheric carbonic anhydride over both land and sea surfaces ; 
on the former by liberating the gases of the soil, and on the 
latter by causing decomposition of the bicarbonates, according to 
Schleesing’s theory. 
Moreover, the advent of a low pressure system is usually 
attended with an increase in temperature, the effects of which 
should augment those occasioned by the diminished pressure. 
Therefore, in that portion of the front of an advancing cyclone, 
which is characterized not only by fall of pressure, but by increase 
of temperature and calm—and which appeals to our senses by 
the warm, muggy feel of the air, the smell from sewers, and 
the capping of hills with cloud—an increase in the amount of 
atmospheric carbonic anhydride should occur. “But in other parts 
of the system this effect might be altogether destroyed by the 
force of the wind. 
For no matter what type of weather may happen to prevail, an 
increase in the wind’s force ought, we think, to lead to a diminu- 
tion of the amount, owing to the agitation of the different air 
strata and the resulting rapid admixture of the pure with the 
impure. Very few of the observers who have studied the question 
of atmospheric carbonic anhydride appear to have considered their 
results in relation to the prevalent type of weather, and their 
position at the time of observation on a synoptic chart, though the 
subject is worthy of attention; and here, of course, the method 
of determination is of importance, for it is obvious that what is 
required is the amount of carbonic anhydride at a particular time, 
and not the average amount during a considerable interval. Hence, 
