42 



PROCEEDINGS OF THE AMERICAN ACADEMY 



With these three orifices, the horizontal elements of the surfaces, 

 bounded by their edges, vary from being parallel with the axis of the 

 stream to a maximum deviation therefrom of 0° 33' in each of the ori- 

 fices at Station No. 5, and of 0° 31' at Station No. 9. 



The direction of the deviation of the surfaces being such that at 

 Station No. 5 the particles of water in passing would impinge upon it, 

 and at Station No. 9 they would withdraw from it. 



The effect of these slight deviations is presented in the following 

 table, and in Fig. No. 2 of Plate No. 3 : — 



From these results, we see that, where the surface included by the 

 edges of the orifice is turned, even very slightly, so that the particles 

 of water flowing parallel with the axis of the stream strike into it, 

 the surface of water in the piezometer stands higher than the surface 



