Exponential formulas have been developed as the result of experiments which have demonstrated that _V_ does not vary as the one-half power of _R_ and _S_ but that the relation should be expressed as, _V_ = _CR_^{_p_}_S_^{_q_}, in which _p_ and _q_ are constants and _C_ is a factor dependent on the character of the material. The various formulas coming under this classification have been given the names of the experimenters proposing them. Examples of these formulas are: Flamant’s, in English units, for new cast-iron pipe, which is, _V_ = 232_R_^{.715}_S_^{.572}, and Lampé’s for the same material which is, _V_ = 203.3_R_^{.694}_S_^{.555}. These formulas are useful only for the material to which they apply, but they can be used for conduits of any shape. A. V. Saph and E. W. Schoder have shown[31] that the general formula for all materials lies between the limits, _V_ = (93 to 142)_S_^{.50 to .55}_R_^{.63 to .69}. Hazen and Williams’ formula is in the form, _V_ = 1.31_CR_^{.63}_S_^{.54}, in which _C_ is a factor dependent on the character of the material of the conduit. The values of _C_ as given by Hazen and Williams are, _C_ CHARACTER OF MATERIAL 95 Steel pipe under future conditions. (Riveted steel.) Cast iron under ordinary future conditions and brick 100 sewers in good condition. 110 New riveted steel, and cement pipe. 120 Smooth wood or masonry conduits under ordinary conditions. Masonry conduits after some time and for very smooth pipes such as glass, brass, lead, etc., when old, and for new 130 cast-iron pipe under ordinary conditions. This formula is of as general application as Kutter’s formula and is easier of solution, but being more recently in the field and because of the ease of the solution of Kutter’s formula by diagrams it is not in such general use. Exponential formulas are used more in waterworks than in sewerage practice. Manning’s formula is in the form, _V_ = 1.486⁄_n__R_^⅔_S_^½ in which _n_ is the same as for Kutter’s formula. Charts for the solution of Manning’s formula are given in Eng. News-Record, Vol. 85, 1920, p. 837.