p1/G1^([gamma]) = p2/G2^([gamma])
.: p2/G2 = (p1/G1)(p2/p1)^([gamma] - 1)/[gamma]
v2²/2g = (p1/G1){[gamma]/([gamma] - 1)} {1 - (p2/p1)^(([gamma] - 1)/[gamma]}; (1)
or
v2²/2g = {[gamma]/([gamma] - 1)} {(p1/G1) - (p2/G2)};
an equation commonly ascribed to L. J. Weisbach (_Civilingenieur_,
1856), though it appears to have been given earlier by A. J. C. Barre
de Saint Venant and L. Wantzel.