144 UNIVERSITY OF VIRGINIA PUBLICATIONS 



There is but little choice between these six forms for the limits prescribed 

 above; thej' are however given in the order of respective merit. The con- 

 stants which enter as exponents have been chosen from the nearest one of 

 Ij y%) Vsj ™ order that the tables of square and cube roots may be used 

 in the computations. There appears to be no advantage to be derived 

 from using other numbers than these. In the evaluation of X the constant 

 .0002 was assigned from experiments on very small tubes of glass, brass 

 and zinc. For pipes of iron the sequel will show that the value of A should 

 be .0001. 



In the Table II are entered under V the observed velocity, D the known 

 diameter, 100 m, the observed value of m. In the columns headed 100 m^. 

 100 TOa. 100 '»3 ^e entered the computed values of m from the respective 

 formula (35), (36), (37). Under the columns headed lOOnit and lOQm^ 

 are entered the corresponding values of m as taken from the tables of J. T. 

 Fanning and of Hamilton Smith, Jr., as given in T. & E., respectively. 

 From 1 — 18 the experiments are by H. Smith, Jr., on sheet iron asphaltum 

 coated pipes at Forth Bloomfield, California, taken from Fanuing-'s book, 

 p. 236. From 18 to 46 the experiments are by Darcy, quoted by Fanning, 

 p. 237, as clean cast iron pipes. From 46 to 58 the experiments were by 

 J. T. Fanning (p. 338) on wrought iron cement lined pipe. From 58 to 65, 

 in which the discrepancies are somewhat larger, the experiments are by 

 Couplet on a compound pipe at Versailles, composed partly of stoneware 

 and partly of lead, in fair condition, H. & T. p. 136. From 65 to 79 the 

 experiments were by Weisbach, given in his Mechanics of Engineering, 

 Appendix, Coxe's translation, p. 1100; the first six are glass tubes, the 

 next four of brass and the remainder of zinc. In the Smith-Coffin graphical 

 table used the velocities are tabulated only up to 10 feet, and the curves 

 not generally drawn for velocities less than 0.5 feet. These examples thus 

 tabulated cover a sufficiently wide range of material and velocities as well 

 as diameters to exliibit the general behavior of the formulae for 7n and 

 their agreements with each other and a rather miscellaneous collection 

 of experiments, to justify a further and subsequent differentiation into 

 classes. It was not thought worth while to tabulate computations of m^, 

 m^, nie, as these do not agree in general so well as the first three forms. 



