. Elementary lessons in the physics of agriculture . Fig. J,6. differences of temperature of rolled and unrolled soil and associated air tempei t. - tares. The air receives more heat from the unrolled ground for two reasons. 1. Its many lumps present a much greater contact surface. 2. The lumps being dry become warmer at the surface than the more moist rolled soil. Further than this, the lumps, being in poor connection with the soil below, conduct their heat slowly downward while at the saT'.e time they shade the lower soil; and by exposing a very large surface to the sky they cool rapidly by
. Elementary lessons in the physics of agriculture . Fig. J,6. differences of temperature of rolled and unrolled soil and associated air tempei t. - tares. The air receives more heat from the unrolled ground for two reasons. 1. Its many lumps present a much greater contact surface. 2. The lumps being dry become warmer at the surface than the more moist rolled soil. Further than this, the lumps, being in poor connection with the soil below, conduct their heat slowly downward while at the saT'.e time they shade the lower soil; and by exposing a very large surface to the sky they cool rapidly by radiation. The measured differences of soil temperature due to this cause have been as great as ° to 10° F., the lower figure having been observed at a depth of three inches and the higher at inches. The heating effect of fermenting manures in the soil has been observed to produce a rise in temperature of nearly 1° F. In the case of well drained soil the percolation of warm summer rains often carries rapidly and deeply into the soil considerable heat and thus raises the temperature directly, and as this water must evaporate more slowly from the drained soil, if at all, than from the undrained, it is not cooled as much as it might have been had percolation not occurred, thus leav- ing all the water to evaporate in a short time.
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishermadis, bookyear1894
