APPENDIX B. THE DISCHARGE-MEASURING GATE AND ITS RATING. 



THE GATE. 



The gate for measurement of discharge is 

 mentioned at page 20, and its general relation 

 to other apparatus is shown in figure 2. In a 

 section on the measurement of discharge, page 

 22, it is briefly described, and the history of its 

 use is outlined. Figure 88 is designed to ex- 

 hibit its relations more fully and shows the 

 arrangement of the general apparatus of the 

 laboratory at the time of its calibration. 



The gate controlled an opening in the side of 

 a vertical wooden shaft, of which the internal 

 horizontal section measured 3 feet by 0.5 foot. 

 At the top the shaft communicated freely with 

 a long, narrow tank, to which water was con- 

 tinuously delivered by a pump. The surface 

 level of water in the tank was regulated by 

 means of an overflow weir and a valve above 

 the pump and was observed in a glass tube or 

 gage, AB, in figure 88, outside of the tank. 

 This tube was given a slope of 1 in 10, so that 



Overhead tank 



FIGURE 88. Arrangement of apparatus connected with the rating of the discharge-measuring gate. 



the movements of its water column afforded a 

 magnified indication of changes in the water 

 level within the tank. 



Details of the gate are represented to scale 

 in figure 89. A brass plate, PP, attached by 

 screws to the outer face of the shaft, was 

 pierced by an opening of 10.5 by 2 inches, the 

 longer dimension being horizontal. About 

 three sides the edges of the opening were 

 beveled outward, leaving a 45 edge at the 



20921 No. 86 14 IT 



inner face of the plate. A sliding plate, G, 

 rested against the inner face of the fixed plate. 

 This was the gate proper, its function being to 

 close either the whole or a definite portion of 

 the opening and thus regulate the width of the 

 issuing water jet. It overlapped by half an 

 inch the margins of the opening, above and 

 below, and was guided by two brass pieces, 

 which appear in sections 6 and c. To the end 

 adjacent to the water jet was given a chisel 



257 



