[88] Physics of Agriculture, p. 270.

[89] Only a general outline of the principles of this subject is given in this volume; special works must be consulted for working details. Among these the volume by King on “Irrigation and Drainage” gives probably the most comprehensive presentation of the subject for both humid and arid climates. Also bulletins of the U. S. Dep’t of Agriculture.

[90] Published by permission of the Department.

[91] Such tests can be readily made by any one, by digging a pit to four or five feet depth, and supplying water to a shallow basin dug into the surface 8 to 12 inches distant from the vertical wall of the pit. The descent of the water is then readily observed on the vertical side of the pit nearest to the water basin. Preliminary tests with soil probe ([see chap. 10, p. 177]).

[92] [See below, chap. 17].

[93] Bull. No. 21, Bureau of Soils; also circular No. 10, ibid.

[94] Bull. Ariz. Exp’t Sta. No. 44.

[95] Bull. Arizona Exp’t Station Nos. 2, 38.

[96] Progress Report on Coöperative Irrigations in Calif.; Cir. No. 56, Office Exp’t Stations.

[97] Rep. Calif. Expt. Sta. for 1897-98, p. 65.