iS6 Mr. Dalton on the constitution of the atmosphere. 



According to one view. 



2. The altitude of each atmo- 

 sphere differs from that of every 

 other, and the proportions of 

 each in the compound atmo- 

 sphere gradually vary in the 

 ascent. 



3. When two atmospheres are 

 mixed, they take their places 

 according to their specific gra- 

 vity, not in separate strata, but 

 intermixedly. There is however 

 a separate stratum of the speci- 

 fically lighter atmosphere at the 

 summit over the other. 



According to the other view. 



2. The altitude of each atmo- 

 sphere is the same, and the pro- 

 portion of each in the compound 

 atmosphere is the same at all 

 elevations. 



3. When two atmospheres are 

 mixed, they continue so, without 

 the heavier manifesting any dis- 

 position to separate and descend 

 from the lighter. 



All that we have said hitherto has been relating to quiescent 

 atmospheres, or such as are in a state of perfect equilibrium. 

 How the case would be with regard to the earth's atmo- 

 sphere, such as it actually is, in a state of continual motion 

 and agitation greater or less in all its parts, it is not very easy 

 to ascertain ; and it is besides rather a question to be decided 

 by experiment and observation than by any theory. I have 

 a series of observations made on this subject ; but as they 

 will require to be submitted in a considerable detail, I shall 

 reserve them as a sequel to this essay on some future 

 occasion. 



