Mr. Josiah Parkes, one of the leading draining engineers of England, has
made some experiments to test the extent to which draining affects the
temperature of the soil. The results of his observations are thus stated
by Gisborne: "Mr. Parkes gives the temperature on a Lancashire flat moss,
but they only commence 7 inches below the surface, and do not extend to
mid-summer. At that period of the year the temperature, at 7 inches, never
exceeded 66 deg., and was generally from 10 deg. to 15 deg. below the temperature of
the air in the shade, at 4 feet above the earth. Mr. Parkes' experiments
were made simultaneously, on a drained, and on an undrained portion of the
moss; and the result was, that, on a mean of 35 observations, the drained
soil at 7 inches in depth was 10 deg. warmer than the undrained, at the same
depth. The undrained soil never exceeded 47 deg., whereas, after a thunder
storm, the drained reached 66 deg. at 7 inches, and 48 deg. at 31 inches. Such
were the effects, at an early period of the year, on a black bog. They
suggest some idea of what they were, when, in July or August, thunder rain
at 60 deg. or 70 deg. falls on a surface heated to 130 deg., and carries down with it,
into the greedy fissures of the earth, its augmented temperature. These
advantages, porous soils possess by nature, and retentive ones only
acquire them by drainage."
Drained land, being more open to atmospheric circulation, and having lost
the water which prevented the temperature of its lower portions from being
so readily affected by the temperature of the air as it is when dry, will
freeze to a greater depth in winter and thaw out earlier in the spring.
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