TRANSPARENCY OF THE AIR. 19 



It is a highly important fact that the air we breathe does 

 not consist, like water, of an intimate combination of elements, 

 but only of a mixture of gases which are not united together by 

 the close bonds of chemical affinity. The reduction or sepa- 

 ration of a compound body whether solid, liquid, or gaseous 

 into its component parts is in every case the more or less 

 violent disruption of a more or less intimate association, and con- 

 sequently cannot be effected without the waste or consumption 

 of a certain amount of power. Thus we see how greatly the 

 respiratory process of animals is facilitated by their being able 

 to obtain their supply of oxygen, without first being obliged to 

 separate it from an intimate connection with its accompanying 

 nitrogen, which, going in and out of the lungs unchanged, merely 

 performs the passive but highly important part of moderating 

 the action of its fiery partner. 



The air of the atmosphere not only contains the substance 

 which our vital process absolutely requires for its maintenance 

 but its physical properties have likewise been made to harmonise 

 most beautifully both with the existence of organic life and the 

 development of our mental powers. What would have been the 

 consequence if, instead of allowing a free passage to the calorific 

 rays of the sun, it had been a ready absorber of their warmth ? 

 Then the heat which is necessary for the growth of plants would 

 never have reached the surface of the earth, but have been swal- 

 lowed up, and again radiated into space by the upper regions of 

 the atmosphere. 



The wonderful transparency of the air not only allows us to 

 see terrestrial objects at a great distance, such as a ship rising 

 at the brink of the horizon, or a mountain-peak raising its snow- 

 clad summit above many miles of intervening country, but to 

 penetrate through the whole of its crystal depths to those far- 

 distant worlds which so magnificently bespangle the dark vault 

 of heaven, and whose study forms one of the noblest occupations 

 of the human mind. 



As the bearer of sounds which undulate along on its elastic 

 waves, the air likewise largely contributes to the enjoyment of 

 life and to our intellectual improvement. Our eye might ever 

 so much delight in the aspect of a beautiful landscape, the scene 

 would still seem desolate and dreary if it lay before us in deep 

 uninterrupted silence. 



The waving corn-field, the rustling grove, would be bereft of 



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