84 BULLETIN 376, U. S. DEPAETMENT OF AGRICULTURE. 



Page 79, line 27. The writer would here call attention to the importance of deter- 

 mining accurately the average diameter at each point of manometer attachment. A 

 very slight difference between the areas at the two points will make a very considera- 

 ble difference in the results, particularly if the total difference in head between the 

 two points is relatively small. An examination of the data relating to the test of the 

 54-inch pipe. No. 44 (Trans. Amer. Soc. Civ. Engin., vol. 49, 1902) will show a very 

 considerable change in area throughout the length of the pipe. It was found that the 

 velocity head at any point was exactly proportional to the calculated velocity head. 



Page 64, line 40. Same reference is made as for page 60, line 17, as the best 

 means of preventing loss at the entrance and exit. This funnel-shaped entrance pre- 

 vents the trapping of air at the entrance caused by excessive suction and cross cur- 

 rents, but does not prevent the minute particles of air flowing with the water, or the 

 air that is absorbed by the water, and does not leave it until under a greater pressure 

 from entering the pipe line. Accumulation of air from these causes must be taken 

 care of either by standpipes or automatic relief valves. To leave it in the pipe when 

 there are high points in the pipe line and low velocities is to seriously diminish the 

 flow. It is the writer's opinion that many of the inconsistent results from various 

 tests are due to this cause. 



Page 73, line 35. In the case of pipe used for irrigation purposes where the entrance 

 is direct from a ditch, with no adequate settling basin, a considerable quantity of silt, 

 moss, and other debris traveling along the bottom of the ditch finds its way into the 

 pipe line and accumulates in the low points of the pipe, even at velocities higher 

 than 5 feet per second. It becomes settled and packed and slimed over at times 

 when the velocity in the pipe is low. The moss and other vegetable matter tend to 

 bind the silt together into a solid mass, which is not washed out by the higher veloc- 

 ity. This is probably what happened to the pipe line in question. 



Page 79, line 31. There were three gauges used in these experiments: 

 (a) A hook gauge located at the settling basin or discharge end of the pipe. 

 (6) A water manometer attached to the top of the pipe about 150 feet upstream from 

 the outlet end. Sufficient readings were taken at manometer B to make a check 

 on accuracy of using the hook gauge. 

 (c) A water manometer located 232 feet downstream from the intake. The area of 

 the pipe at the exit was slightly larger than at manometer B. The head of 

 water at manometer B , less the friction in the pipe line between manometer B 

 and the settling basin, less the difference in velocity head, equaled the head 

 at the settling basin or exit end within the limits of possible error from other 

 causes. 



Page 79, line 36. The velocity measurements at the exit of the 54-inch pipe revealed 

 some interesting facts regarding the flow in pipe lines as follows: 



First. That the line of maximum flow of water in a pipe line beyond a bend is not 

 in the center of the pipe, but near the outer circumference, and on the same side as 

 the convex side of the curve in the pipe. This would seem to be due to the action 

 of centrifugal force of the water in going around the curve, tending to crowd the max- 

 imum velocity toward the outer edge of the curved portion of the pipe. 



Second. The average velocity as determined from a number of points distributed 

 systematically throughout the area of the circle of the pipe is the same as the average 

 velocity along either the vertical or horizontal diameter. 



Third. The curve of velocity, as near as the writer could determine, is an ellipse 

 where the maximum velocity is in the center of the pipe. 



Mr. Henny: The results of the experiments on flow in wood pipe made by the 

 author, under the direction of Mr. Fortier,' constitute much needed addition to the 



1 Author's footnote. — Samuel Fortier, Chief of Irrigation Investigations, Office of Public Roads and Rural 

 Engineering, U. S. Department of Agriculture. 



