OF ARTS AND SCIENCES. 41 



the trough that careful observation detected no variation therefrom, 

 and having areas in circular form from 0.0003 sq. ft. to 0.0054 sq. ft., 

 and one rectangular area having a height of 0.083 ft. and a length of 

 0.33-1 ft., there was no lowering of the piezometric column by cohe- 

 sion of the water acting at its base ; and shows that the height of the 

 piezometric column was in excess of that of the stream by an amount 

 extremely small, but with large velocities it was within the practicable 

 limits of observation. 



Orifices slightly inclined. Passages normal. 



Before concluding the result just obtained to be a general truth, it 

 is important to learn in what manner it will be affected by slight 

 modifications of the conditions under which it was obtained. These 

 are fortunately presented, probably through unequal swelling of the 

 wood, in the orifices on each side at Station No. 5, and at the west 

 orifice at Station No. 9. 



After the experiments were made, those with high velocities being 

 recently completed, these orifices were found to be in the following 

 condition : — 



At Station No. 5, the orifice upon the west side being a rectangle 

 0.337 ft. high and 0.084 ft. wide, horizontally, had its top, bottom, 

 and down-stream edges well in the plane of the side of the trough ; 

 but the up-stream edge, being in this plane at the top and bottom, 

 receded from it 0.0008 ft. at its mid height. The orifice upon the 

 east side, being a rectangle 0.336 ft. high and 0.021 ft. wide, horizon- 

 tally, was in the condition that the plane of the side of the trough for 

 half a foot up stream from the orifice continued across it would cut 

 into the down-stream side of the orifice about 0.0002 ft. back from its 

 edge, for about two-thirds of the lower part of its height. 



It is probable that these variations from a plane increased during 

 the three months in which the experiments were made, in which case 

 the condition presented is not applicable to the earlier experiments 

 with small velocities. 



At Station No. 9, the orifice in the west side was cut 0.168 ft. high 

 and 0.250 ft. long, and then filled for the up stream one-third of its 

 length by a block, leaving a square orifice. At the end of experi- 

 ments, the edges of the original orifice were found to be in the plane 

 of the side of the trough, and the up-stream and top edges of the block 

 were also in this plane ; but the lower down-stream corner of the 

 block, and consequently the lower end of the up-stream edge of the 

 orifice, projected into the trough 0.0015 ft. 



