developed a formula that best fitted the data. The first best-fit formula was the following: He then simplified this formula to: In 1885, Manning gave the value of 2/3 and wrote his formula as follows: In a letter to Flamant, Manning stated: "The reciprocal of C corresponds closely with that of n, as determined by Ganguillet and Kutter; both C and n being constant for the same channel." On 4 December 1889, at the age of 73, Manning first proposed his formula to the Institution of Civil Engineers (Ireland). This formula saw the light in 1891, in a paper written by him entitled "On the flow of water in open channels and pipes," published in the Transactions of the Institution of Civil Engineers (Ireland). Manning did not like his own equation for two reasons: First, it was difficult in those days to determine the cube root of a number and then square it to arrive at a number to the 2/3 power. In addition, the equation was dimensionally incorrect, and so to obtain dimensional correctness he developed the following equation: where = "height of a column of mercury which balances the atmosphere," and was a dimensionless number "which varies with the nature of the surface." However, in some late 19th century textbooks, the Manning formula was written as follows: Through his "Handbook of Hydraulics," King (1918) led to the widespread use of the Manning formula as we know it today, as well as to the acceptance that the Manning's coefficient should be the reciprocal of Kutter's . In the United States, is referred to as Manning's friction factor, or Manning's constant. In Europe, the Strickler is the same as Manning's , i.e., the reciprocal of . References External links History of the Manning Formula 1816 births 1897 deaths Irish civil engineers