3. Our author very justly states, that the _gaseous_ state of the atmosphere is owing to the quantity of _caloric_ in combination, the entire _abstraction_ of which would render our atmosphere a body as solid as the diamond. This caloric is not imparted to it by the beams of the sun _passing through_ it; because, radiant matter does not warm gaseous bodies by passing through them. This caloric is chiefly supplied from the _earth_, by the lowest stratum of air coming in contact with it, and when heated ascends, and thus gives place to a colder stratum. Hence the air is much warmer at the surface of the earth, than in its higher regions. 4. Our author inclines to the opinion that the atmosphere is the product of a _chemical_ combination of the gases, yet great names, and weighty arguments are in favor of the opposite theory of a _mere mixture_ of gases. 5. There is one point not presented in the preceding section. It is well known that oxygen is abstracted from the air by _combustion_, and the _breathing_ of animals. This abstraction is very large. From whence then comes the supply of oxygen sufficient to keep up the constitutional quantity of this gas in the atmosphere? The only answer I have met with to this difficult question is this: The _growing of vegetables_ is supposed to supply it, as it is well known that they absorb carbonic acid during the day, and evolve oxygen. But it is also well known that this process is _reversed_ during the night. Hence it would appear that this is not a sufficient cause. Still it would seem there must be a sufficient supply from some source, as chemists have not been able to detect any change in the constitution of the air. May not the oxygen be _restored_ back again by _evolution_ from those bodies which have _absorbed_ it, _upon their decomposition_? Thus there would be a successive absorption and evolution as the process of nature went on; which would tend to keep up an equal distribution of oxygen.] * * * * * Footnotes - Chapter III [53] Dr. Clarke on Gen. i, 6. [54] Benson on Gen. i, 6. [55] Dalton’s New System of Chemical Philosophy, part 1, p. 1. [56] Lavoisier’s Elements of Chemistry, p. 78. [57] Manchester Memoirs, New Series, vol. i, p. 254. [58] When solid substances are rendered permanently aëriform by heat, the air thus produced is called a _gas_. John Baptist van Helmont, a physician and chemist, born at Brussels, in 1577, and educated at Louvain, was the first chemist who made use of this term to denote an elastic fluid. He gave fixed air the name of _gas_.