FLOW OF WATER IN CLEAN PIPES 253 



is scaled the values of 1000s or lost head in 1000 feet of length. A straight 

 line (preferably a transparent straight edge or black silk thread) through 

 and a point on the slope scale cuts the diameter curve in a point whose 

 abscissa is at once the velocity read to hundredths, the ordinate of such 

 a point is the value of the coefficient k. In all the plates the curves are 

 drawn for diameters in inches and feet and not for the hydraulic radius. 



10. The regulation of the Society regarding the length of its pubhshed 

 papers prohibits me at this time from giving the corresponding results 

 for open channels. The improved formula has however been extended 

 to include these cases with corresponding satisfactory results which reduce 

 the number of classes of roughness to one half the number given in the 

 previous paper. This I hope to present at some time in the near future. 



11. Provisional formula. If Plate III be closely examined, the lines 

 corresponding to given diameters which give the values of the coefficient 

 k computed from (14) are practically straight lines of uniformly increasing 

 slopes. It is easy to design a formula that will give the values of k with 

 practical accuracy in terms of r and V, thus 



k={r + 0A)V+6Q + 4:5r -%^- (l6) 



?' + 0.1 



Since V = fcVs, there results for the value of V in terms of r and s 

 the formula 



60 + 45r 



r + 0.1 ,- , , 



V = — , , »,w- ^s, (17) 



1- (?- + 0.4)Vs ' ^ ^ 



a formula easy to compute and practically accurate. 



