Marlborough, in the year 1898, by Z. J. Drake; and, according to the
authentic report of the official committee that measured the land
and saw the crop harvested and weighed, and awarded Drake a prize of
five hundred dollars given by the Orange Judd Publishing
Company,--according to this very creditable evidence, that acre of
land yielded 239 bushels of thoroughly aid-dried corn; and such a
crop, Mr. Thornton, would require as much carbon as the total amount
contained in the air over an acre of land."

"Well, that is astonishing! Then there must be some other source of
supply besides the air."

"There is no other direct source from which plants secure carbon;
but of course the air is in constant motion. Only one-fourth of the
earth's surface is land, and perhaps only one-fourth of this land is
cropped, and the average crop is about one-fourth of three tons; so
that the total present supply of carbon in the air would be
sufficient for about two hundred and fifty years. But as a matter of
fact the supply is permanently maintained by the carbon cycle. Thus
the carbon of coal that is burned in the stove returns to the air in
carbon dioxid; and all combustion of coal and wood, grass and weeds,
and all other vegetable matter returns carbon to the atmosphere. All
decay of organic matter, as in the fermentation of manure in the
pile and the rotting of vegetable matter in the soil, is a form of
slow combustion and carbon dioxid is the chief produce of such
decay. Sometimes an appreciable amount of heat is developed, as in
the steaming pile of stable refuse lying in the barnyard, while the
heat evolved in the soil is too quickly disseminated to be apparent.

"In addition to all this, every animal exhales carbon dioxid. The