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130 PROCEEDINGS OF SECTION B. 
sphere, and agencies exist there to determine their combina- 
tions; but we have disturbing influences operating which 
are not taken into account gn these calculations. 
We have seen what broad and enlightened views respect- 
ing the complicated character of atmospheric air have been 
held by some of the ablest thinkers of remote and recent 
centuries, and we have considered how far modern scientific 
research has been confirming and expanding these views by 
rigid demonstration; but, far as the modern scientists have 
led us, they have only opened up fresh avenues of investiga- 
tion. 
Arr TRAFFIC. 
Experiment has abundantly demonstrated that the pro- 
portions of the chief ingredients of the air remain wonder- 
fully constant all over the world; experiment has also con- 
firmed, what observation and reasoning have for so long sug- 
gested, that the composition of the atmosphere in every place 
is undergoing ceaseless change. There is a stupendous and 
constant traffic in air and its constituents. Just as all 
waters tend to flow into the sea, so gases, unless imprisoned, 
flow into the air. The atmosphere is their natural reservoir. 
We know that gases of many kinds are produced all over 
the earth. We have carbon dioxide from some fermenta- 
tions and decompositions; we have hydrogen and marsh-gas 
and similar substances from others; sulphuretted hydrogen, 
phosphuretted hydrogen, &c., as results of decay ; gases from 
volcanoes; gases imprisoned in stones; gases in the waters 
of springs, lakes, rivers, of the sea; gases in the arable land, 
and in the porous strata. All these gases, when permitted, 
escape into the air. The vapours of most, if not all, liquids 
pass into the air, and the vapours of at least many solids; 
besides these, we have liquids and solids in various states of 
exceedingly fine division, finding their way into at least the 
lower portion of the atmosphere, and sometimes into the 
higher reaches. 
But there is a return traffic. Rain, dew, snow, hail, and 
all such results of condensation and precipitation, dissolve 
up, or include or entangle the gases of the atmosphere in pro- 
portions depending upon temperature, pressure, and other 
varying conditions. We have only to follow a shower of 
rain. In condensing, and falling through the air, it has 
dissolved up some of the gases, and washed out certain 
vapours and many of the solid and liquid particles which the 
air has been holding in suspension. 
Falling on the ground, part, as we all know, is absorbed 
through being soaked up by more or less porous soil or rock, 
