OF ARTS AND SCIENCES. 



29 



through its successive steps to increase the velocity of the water 

 passing through it. 



Starting four feet from the entrance, cross bars of wood 0.9 ft. long, 

 0.1 ft. wide, and 0.15 ft. deep, were screwed to the top of the trough at 

 intervals of just 2.5 ft., the top of the trough being let up into them 

 0.05 ft. 



The up-stream top edge of each cross bar was taken as a station, and 

 these were numbered from 1 to 1 1, beginning with the up-stream cross bar. 



Under the projecting ends of the cross bars were attached, to the 

 outer surface of the two-inch planks which made the sides of the 

 trough, tin boxes about 0.9 ft. long, 0.5 ft. wide, and 0.9 ft. high, hav- 

 ing blocks of wood fastened within some of them, as shown upon the 

 plates, to reduce the free surface area of water which they would con- 

 tain. These boxes, serving as reservoirs, and called still-boxes, were 

 put in communication with the interior of the trough by passages hav- 

 ing orifices of various forms and dimensions, and being variously dis- 

 posed, as expressed in the following table : — 



