4» PROCEEDINGS OF THE AMERICAN ACADEMY 



ing 6 ft. per sec. "With velocities between seven and' one half feet 

 and eight and one half feet per sec, the average height in the reservoir 

 was greater than that at the middle of the stream by 0.0108 ft. 



But, immediately upon projecting one of the pipes into the stream, 

 a marked change is observed : the surface in the reservoir is imme- 

 diately lowered ; with a velocity of 2.77 ft. per sec, the westerly pipe 

 being flush with the side, the surface in the reservoir was 0.0011 ft. 

 higher than that in the stream, but, upon projecting this pipe 0.013 ft. 

 into the stream, the surface in the reservoir immediately lowered to 

 0.0259 ft. below that of the stream; the mean velocity continuing 

 2.80 ft. per sec. With the same projection of 0.013 ft., with veloci- 

 ties from 2.09 ft. to 8.35 ft. per sec, the lowering of the surface of 

 the reservoir below that of the stream increased from 0.0187 ft. to 

 0.2196 ft. in a series expressed approximately by heights equal to 

 0.0033 U% as shown in Fig. No. 4, Plate No. 3. 



Increasing the jirojection to 0.055 ft., the mean velocity being 

 7.95 ft. per sec, the lowering of the reservoir was 0.4392 ft., or 

 0.00G9 U' 1 ; and it would probably have been more, but at this height 

 the surface of the reservoir was drawn below the top of the pipe, even 

 to its centre, and air was drawn into the stream. 



The form of the stream of air at the orifice revealed to the eye the 

 cause of the lowering in the reservoir. It was evident that the par- 

 ticles of water striking the up-stream side of the pipe were deviated in 

 part nearly at a right angle toward the middle of the stream, and 

 their course again bent down stream, forming a path approximating 

 a quadrant of an ellipse whose conjugate axis lay in the end of the 

 pipe parallel with the axis of the stream. 



Upon withdrawing the pipe and reducing the projection to 0.007 ft., 

 the lowering in the reservoir is expressed by 0.0011 W 1 . 



At the east side, with the pipe so placed that its most projecting 

 point was in the plane of the side of the trough, and with a mean 

 velocity of stream of 7.95 ft. per sec, the surface of water in the 

 reservoir was 0.0009 ft. above that of the stream ; but, upon projecting 

 the pipe 0.008 ft., the surface in the reservoir was lowered to 0.1080 ft. 

 below that of the stream, the mean velocity continuing 7.98 ft. per 

 sec. This lowering may be expressed by 0.0017 U 2 . 



Upon projecting this pipe 0.012 ft., the lowering, with a mean 

 velocity of 7.86 ft. per sec, amounted to 0.1797 ft., or 0.0029 XJ-. 



If we knew the actual distribution of velocities throughout the 

 stream, it would be interesting to trace the relation of the lowering of 

 the reservoir and the velocity of the stream just at the end of the pipe. 



