_Overhead Spray Irrigation._--The most satisfactory garden irrigation is the overhead spray system. Posts are set ten feet apart in rows 50 feet apart. Water pipes are laid on the tops of the posts and held loosely in position by large staples. These water pipes are perforated by drilling a line of small holes about three feet apart in a straight line along one side of the pipe. The holes are tapped and small brass nozzles are screwed in. The overhead pipes are connected with standpipes at the highest place, generally at the ends of the rows. The pipe-lines are loosely coupled to the standpipes to permit them to roll partly around to direct the hundreds of spray nozzles as needed. [Illustration: Figure 127.--Overhead Irrigation. Diagram showing the arrangement of pipes for irrigating one acre of land. The pipes are supported on posts six feet high.] Six feet high is sufficient to throw a fine mist or spray twenty-five feet, which is far enough to meet the spray from the next row, so the ground will be completely covered. To do this the pipes are rolled from one side to the other, through a 90 degree arc to throw the spray on both sides. The pipes usually are laid with a grade which follows down the slope of the land. A fall of one foot in fifty is sufficient. Water is always admitted at the upper end of each pipe-line to flow down by gravity, assisted by tank pressure. A pressure of about forty pounds is needed to produce a fine spray, and to send it across to meet the opposite jets. The little brass nozzles are drilled with about a one-eighth inch hollow. But the jet opening is small, about No. 20 W. G. This gives a wire-drawn stream that quickly vaporizes when it meets the resistance of the atmosphere. When properly installed a fine misty rain is created, which quickly takes the same temperature as the air, and settles so gently that the most delicate plants are not injured.