218 THE CHEMISTRY OF CREATION. 



than the lighter, and, more singular still, actually 

 with as much force as if they were rushing up 

 into a vacuum ! Thus they have power to rise 

 to the very highest regions of our atmosphere, 

 and to spread to its remotest limits. 



It would be difficult to select a more striking 

 illustration of the wisdom and design displayed 

 in assigning laws to the atmosphere, and to 

 gaseous fluids in general, than is thus presented 

 to us. The uniformity of the atmosphere is 

 mainly due to the incessant influence of this 

 dispersive force. Diffusion is, as it were, the 

 messenger between man and vegetation, for it 

 conveys to the one the carbonic acid produced, 

 and brings back to the other the oxygen 

 restored. By this means, also, is gradually 

 effected the dispersion of all gases, no matter 

 whether dense or rare. While the heaviest 

 vapours are thus made to rise and spread far 

 and wide, the lighter ones are also caused to 

 descend and intermix with air far more dense 

 than themselves. These are facts which expe- 

 riment has amply proved. 



De Saussure found the heavy gas of which 

 we have spoken (carbonic acid) present in the 

 thin air of the Alpine summits, and even in 

 greater abundance than in the air of the low- 

 lands far beneath an effect due, without doubt, 

 to the influence of vegetation ; thus clearly 



