-1859] WRITINGS OF JOSEPH HENRY. \Q\ 



diflused through the other; this would give a ready explan- 

 ation of the diffusion of the two gases through each other in 

 close vessels. But it does not seem to us to be applicable to 

 the explanation of free atmospheres co-existing on the sur- 

 face of the earth, as appears to be th§ case, particularly with 

 reference to the gases and aqueous vapor of the atmosphere. 

 I have dwelt upon this point because very erroneous ideas 

 are frequently entertained as to the theory of Dalton, which, 

 whatever may be its truth, has had a very important bear- 

 ing on the progress of meteorology. By one class of writers 

 on the subject it has been the basis of all investigation, and 

 by another it has been too much neglected. All our hygro- 

 metrical calculations relative to the amount of water in the 

 air rest upon it. While there remains but little doubt that 

 if the air, as a whole, were at rest, and sufficient time were 

 given for the establishment of an equilibrium, the several 

 ingredients would arrange themselves in accordance with 

 this theory; yet, since the atmosphere is constantly agitated 

 with currents, and diffusion is carried on more rapidly 

 through this agency than that from the self-repulsion of the 

 atoms, we can onl}'' suppose that there is merely a constant 

 tendency (particularly in the lower strata of the atmosphere) 

 to assume the statical condition indicated by the theory. 



Composition of the Atmosphere. — At the level of the sea and 

 at all accessible heights our atmosphere principally consists 

 of a nearly invariable mixture of two permanent gases, 

 oxygen and nitrogen, and a number of variable substances, 

 of which we enumerate carbonic acid, nitric acid, am- 

 monia, hydrogen, mineral powders, animal and vegetable 

 matter, odoriferous substances, and above all a considerable 

 quantity of water in a state of invisible vapor, and that of 

 partial condensation in the form of cloud. Indeed, it must 

 be a reservoir of all the emanations which arise from the 

 decomposition of animal and vegetable matter, and which 

 are given off from all substances in minute quantities under 

 the application of heat. Though the variable portions of 

 the atmosphere form but a small percentage of the whole 

 mass, yet they exert an important influence on animal and 

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