Letts & Buaxe— The Carbonic Anhydride of the Atmosphere. 199 
Carleton Williams also found an increase in the air of the 
suburbs of Sheffield during snowy weather, and gives the figures :— 
Snow (average of 32 experiments), . . . 3°58 
No snow (average of 110 experiments), . . 3°24 
vy. Fodor, at Buda-Pesth, in an extended series of observations, 
obtained results confirming the above, and gives the following 
averages — 
Mean for 23 days, previous to snow fall, . 3°75 
Mean for 30 days, on which snow fell, . . 3°81 
Puchner, in thetown of Munich, found an increase with snow fall 
and attributes it toa mechanical action of the snow flakes in carry- 
ing down the gaseous products of combustion into the lower 
atmosphere. He also observed an increase during snowy weather 
both in the air of the suburbs and surrounding country districts. 
Lastly, we may give the results of Petermann and Graftiau’s 
observations at Gembloux (Belgium). They found, as a mean of 
seventeen days on which snow fell, 3°10; the general mean for 
Gembloux being 2:94, and the mean for fogey weather 3:13—the 
highest figure representing the effect of any single meteorological 
factor. 
The explanation which they give is that snow (and fog) 
augment the amount by covering the earth with a thick curtain 
of the vapour of water, either vesicular or crystalline, which hinders 
diffusion of carbonic anhydride from the soil into the superior 
layers of the atmosphere. 
It appears to us that such an explanation of the effect of snow 
is improbable, for if it were true, diminution and not increase should 
be the result of snow fall: the layer of snow resting on the surface 
of the ground hindering the diffusion of carbonic anhydride into. 
the air. 
Influence of Wind. 
A number of observers have maintained that the amount 
of atmospheric carbonic anhydride is influenced by wind in one 
or both of two ways, viz. by its direction and by its force. 
Thus De Saussure (at Geneva) gives 3:98 as the average 
