Assume the surveyed head as 240 feet, the water quantity as 207 cubic feet per minute and a pipe line 12 inches in diameter 900 feet long. To ascertain the friction loss, refer to column of pipe diameter and follow across the column for 12 inches diameter to the quantity, 207 cubic feet per minute. The heavy-faced figures above 207 indicate that the loss per 1000 feet of pipe length is 11 feet. Therefore, since the pipe in the example is 900 feet long, the loss will be 11.' × 900/1000 or 9.9 feet, and the effective head will be 240' - 9.9' = 230.1' Steel tubing for supply pipes, from 3 to 12 inches in diameter is listed at from 20 cents to $1.50 a foot, according to the diameter and thickness of the material. Discounts on these prices will vary from 25 to 50 per cent. The farmer can cut down the cost of this pipe by conveying his supply water from its natural source to a pond, by means of an open race, or a wooden flume. An ingenious mechanic can even construct his own pipe out of wood, though figuring labor and materials, it is doubtful if anything would be saved over a riveted steel pipe, purchased at the regular price. This pipe, leading from the pond, or forebay, to the water wheel, should be kept as short as possible; at the same time, the fall should not be too sharp. An angle of 30° will be found very satisfactory, although pipe is frequently laid at angles up to 50°. _Other Types of Impulse Wheels_ In recent years more efficient forms of the old-fashioned overshoot, pitch-back breast, and undershoot wheels have been developed, by substituting steel or other metal for wood, and altering the shape of the buckets to make better use of the power of falling water.