252 UNIVERSITY OF VIRGINIA PUBLICATIONS 



published in the previous paper. For comparison in the columns lOOm 

 and c are recorded these constants as computed from the formula (14). 

 The authoritj^ for the experiment is given and a brief description of the 

 pipe with a reference to where a more complete description can be found. 

 It will be observed that while the formula is designed for clean pipes, 

 straight or of easy curvature, pipes in actual sevice have frequently been 

 used and in some cases even in use for some years when ever it was neces- 

 sary to interpolate a diameter for which a new clean pipe was not found. 

 In other instances for sake of comparison pipes obviously not in this. class 

 have been included. We do not pretend that the same formula without 

 change of constants will give correct results for pipes of smooth lead, tin 

 and glass as well as for riveted iron or cement lined pipes, but we do not 

 have pipes of tin, glass or lead of several feet in diameter nor do we have 

 riveted iron pipes or cement lined pipes from a | to 1 inch in diameter. 

 In fact in actual practice a certain form of construction and material sur- 

 face goes with certain ranges of diameters, which permits a design for 

 the whole group with a fair approximation. The formula constants have 

 been determined to fit the actual performances of pipes in as large a num- 

 ber as could be accumulated regardless of the materials of construction. 

 The only pipes which overlap in sizes are wooden stave pipes, cast iron 

 coated pipes and the riveted iron pipes. The formula fits the riveted 

 iron class and also all the ordinay clean cast iron pipes of service, but 

 a new clean straight asphalted cast iron pipe is smoother and the velocity 

 from the formula (14) should be increased 5 per cent for such a pipe, but 

 when in use a short time the cast pipes belong properly in the same class 

 as the others. The wooden stave pipes are smoother and the velocity 

 computed from (14) should in general be increased 10 per cent for such 

 pipes. 



9. While (14) is complicated in appearance it is easily computable for 

 any particular case being a rational function of r and V. However in 

 order to facilitate its use the writer has computed and carefully drawn 

 the three plates which accompany this paper.* 



Plate I gives the corresponding values of m, V and r and is self ex- 

 planatory. 



Plate II gives the corresponding values of c, V, and r. 



Plate III gives the corresponding values of V, r, s and k where V = 

 k Vs. Along the upper border and down the right border of the diagram 



*Tlie original drawings, 18 by 24 inches, were constructed with precision. The 

 plates in this paper are photographic reductioiis of these accurate drawings and, 

 therefore, may be read with a magnifying glass to advantage. 



