TRIANGULAR NOTCHES 



153 



With these wide-angled notches the value of C, however, fluctuates 

 between much wider limits than in the case of the right-angled notch and 

 this renders the former type not so suitable for measuring purposes. 



Thomson's formula for a right-angled notch may be written in the 

 form 



Q = '305 H* cub. ft. per minute 

 where H is the head in inches. 



A series of very careful experiments has been carried out by Mr. 

 James Barr, 1 on such notches, with heads up to 10 inches. The chief 

 results of these are shown graphically in Fig. 82, where curves C, A, and 



HecucU Inches. 

 FIG. 82. Value of Coefficient C in Q = CH% c.f.m. for a Right-angled Notch. 



B respectively represent the results obtained on a notch with an 

 extremely fine edge, on one with a crest y 1 ^ inch broad, and on one with a 

 crest y 1 ^ inch broad. In these experiments the approach channel was 

 4 feet wide, and the depth of the floor of the channel below the vertex 

 of the notch was 2 feet. 



To find the effect of the width of the channel of approach upon the 

 discharge, false sides made of wood were placed in the flume. They 

 extended the full depth of the flume, and for a distance of 3 feet 

 up-stream. 



Two sets of experiments were made, in one of which a head of 3 inches 

 was maintained and in the other a head of 4 inches. Fig. 83 gives the 

 results. They show that in order that the flow may be independent of 

 the channel width, the latter must be at least eight times the head. 



A sheet of zinc 36 inches broad and 42 inches long was used as a 



1 Mtgineering, April 8 and 16, 1910. 



