. Elementary lessons in the physics of agriculture . 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 m
. Elementary lessons in the physics of agriculture . 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
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