. Graphical and mechanical computation . EXPRESSION INBUERGER RUN-OFF FORMULA. Fig. 586. Akt. 59 FRANCIS FORMULA FOR A CONTRACTED WEIR I09 33 30-. FRA/VC/S FORM = ( H) H $ -/ IS -25 *S \-s Fig. 59. HO NOMOGRAPHIC OR ALIGNMENT CHARTS Chap. V 59. Francis formua for a contracted weir. Q = (B — H) Hk — Here, Q is the quantity of water flowing over weir in cu. ft. per sec., Bis the width of the weir in ft., and H is the head over the crest of theweir in ft. If we write the equation Q — H*B = — H* we have anequation of the form (X), with the s

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. Graphical and mechanical computation . EXPRESSION INBUERGER RUN-OFF FORMULA. Fig. 586. Akt. 59 FRANCIS FORMULA FOR A CONTRACTED WEIR I09 33 30-. FRA/VC/S FORM = ( H) H $ -/ IS -25 *S \-s Fig. 59. HO NOMOGRAPHIC OR ALIGNMENT CHARTS Chap. V 59. Francis formua for a contracted weir. Q = (B — H) Hk — Here, Q is the quantity of water flowing over weir in cu. ft. per sec., Bis the width of the weir in ft., and H is the head over the crest of theweir in ft. If we write the equation Q — H*B = — H* we have anequation of the form (X), with the scales x = m^Q, y = —m2 ( B),Zi = z = —3— — ( if2). Let 5 vary from o to 5, H from o to 8, and Q from o to t,^. If we choose mv = , w2 = , and 7 1 /-. t> I2 ^ .ffs & = 12, our scales are x = (A y = — 2B,zx = —= , z = Hi+ 2 H% + 2 The axes AX and BY are drawn in opposite directions, and the lengthof AB is 12 in. We assign values to H, and on AB we lay off AD = zuand parallel to BY we lay off DD — z, and mark the point thus foundwith the corresponding value of H. We join the points by a smoot

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