. Elementary lessons in the physics of agriculture. Agricultural physics. [from old catalog]. 153 they are shallow, there is inadequate drainage midway be- tween the lines. Why this must be so will be readily seen from an inspection of Fig. 3, for the closer the soil and the more distant the drains, the nearer the surface will the undrained soil approach and the longer will that which is affected remain too Fig. U. ShowiDg the surface of ground-water between tile drains 48 hours after a rain-tall of .87 inch. Since writing the above the actual surface of the ground- water 48 hours after
. Elementary lessons in the physics of agriculture. Agricultural physics. [from old catalog]. 153 they are shallow, there is inadequate drainage midway be- tween the lines. Why this must be so will be readily seen from an inspection of Fig. 3, for the closer the soil and the more distant the drains, the nearer the surface will the undrained soil approach and the longer will that which is affected remain too Fig. U. ShowiDg the surface of ground-water between tile drains 48 hours after a rain-tall of .87 inch. Since writing the above the actual surface of the ground- water 48 hours after a rain fall of .87 inches in a tile- drained field at the Experiment Station which is shown in Fig. 4, has been observed by the writer. In this instance the drains are 33 ft. apart and lie in a medium grained sand overlaid with clay. The height of water above the tops of the tile, midway between the drains, varied at this time, between 4 and 12 inches, and the mean rate of rise was one foot in about 25 ft. ; that is to say, in soil of this character, when the drains are placed 50 ft. apart the ground-water will stand midway between them 48 hours after such a rain, 1 ft. nearer the surface than the drains themselves, and if 100 ft. apart, then 2 ft. nearer the sur- face. It is evident therefore, that the deeper the drains are placed, the further apart they may be and that if tiles are placed 100 ft. apart and 3 ft. deep, the land midway between the lines would not be sufficiently drained because then standing water might reach within 12 in. of the sur- face in parts of the field. It should not be understood that Fig. 4 repi^esents the permanent slope of the surface of standing water in the field in question, for that surface is constantly changing, and in Fig. 5 is shown just how the surface did change be- tween the dates given in the cut, the three broken*^lines. Please note that these images are extracted from scanned page images that may have been digitally enhanced for reada
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