45$ Atiali/ses of Books, [Dec. 



mon hypothesis of the chemical union of mixed gases, and to 

 substitute in its room a theory better according with observed 

 phenomena, and estabhshed by a series of new and important 

 experiments. The leading principle of this theory is, " that the 

 particles of one gas are not elastic or repulsive in regard to those 

 of another gas, but only to the particles of its own kind." Hence 

 it is inferred, that the gases which constitute our atmosphere 

 exercise no further action upon each other than a mechanical 

 opposition when in motion. The aqueous vapour will then be 

 subjected to no additional pressure by commixture with a per- 

 manently elastic fluid. It will, however, be greatly modified by 

 the temperature of the gaseous atmosphere. For example, at 

 an elevation of 5000 feet, the density of an unmixed atmosphere 

 (that at the surface being taken as unity), would be 0*897 of an 

 inch, and its temperature consequently 76*5° Fahr. The tem- 

 perature of an atmosphere of a permanently elastic fluid would 

 however, at the same elevation, be only 64*4°. A mixture of the 

 two atmospheres must then be necessarily accompanied by a 

 condensation; for vapour of '897 density could not subsist at a 

 temperature of 64*4 . Supposing this condensation to have 

 taken place, and each stratum of air to possess the exact quan- 

 tity of moisture due to its temperature, the two atmospheres will 

 still be in a state of intestine motion. For the elasticity of the 

 vapour formed at the surface of the sphere not being counter- 

 balanced by an equivalent pressure from above, that vapour 

 must be continually ascending into the higher regions of the 

 atmosphere, where it will be condensed, and will give out its 

 heat to the ambient air. A reference to our former example 

 may serve to elucidate this general position. It appears from 

 the calculations of Mr. Daniell, that the natural state of an 

 atmosphere of pure aqueous vapour diffused around a sphere of 

 the uniform temperature of 80°, would require, at the elevation 

 of 5000 feet, vapour of the density '897. Under these circum- 

 stances, the pressure of the superior strata would exactly balance 

 the upward tendency of the lower, and perfect rest would neces- 

 sarily result. But in a mixed atmosphere, it has been already 

 shown, that the density of vapour, at an equal elevation, would 

 be only -636, or what is due to the temperature of 64°. Hence 

 the pressure of this vapour will not be adequate to counteract the 

 expansive force of the lower strata. Therefore the vapour formed 

 at the surface will ascend into the colder regions, will be there 

 condensed, and will impart its constituent heat to the surround- 

 ing medium. Here then is to be found the partial source of 

 heat, to which a tacit reference has been made in the first part 

 of the essay. The elasticity of the higher strata of the atmo- 

 sphere will be augmeiited by this accession of temperature, and 

 the velocity of the equatorial current will receive a dispropor- 

 tionate increase. To the irregularities of pressure thus produced 

 are attributed by Mr. Daniell the fluctuations of the barometer. 



