Parky. — Resistance to Flow of li'ater through /'/pes. 49 



the plate at the joint alternately facing and not facing the stream ; in 

 the other case we have the plate or section tapering from a large end to 

 a small end hy twice the thickness of the plate, whilst none of the joints 

 face the stream. There is further the disturbance arising out of the 

 different thickness of plate used, and in comparing two riveted pipes 

 of different diameter it will be realized that they are not similar in 

 all respects unless the thickness of plate bears some proportion to the 

 diameter. The same remarks apply generally to spirally riveted pipe. 

 The principle involved demands that for the same values of vd at the 



same temperature the same value of shall be obtained ; but unless the 



v' 2 



frequency of jointing and the nature of the joints is the same, and unless 



there is a proportionality between diameter, thickness of plate, and size 



of rivet, it cannot be expected that the principle can be strictly applied, or 



that it can be proved to be applicable at all unless the characteristics 



mentioned are taken into account. 



In spite of the vast array of experiments upon pipes of different 

 kinds, it will be found that few of them are of much assistance in the 

 present investigation. The characteristics of the pipe are not always 

 precisely defined. The experiments on any one set are usually not 

 numerous enough, or, if numerous, do not cover a sufficient range. 

 Those experiments that are at all suitable have been used in the present - 

 paper, and a study of the diagrams will afford an indication as to the 

 scope which should be given to further experiments. 



In addition to the disturbing factors arising out of the nature of 

 the surface, and frequency and nature of the joints, the thickness of plate 

 in riveted pipe, and riveting, there is evidently another disturbing element 

 arising out of the elastic compression of the water and from the accelera- 

 tion and retardation of the flow. Most of the available observations 

 on large pipe have been obtained under working conditions, and subject 

 to disturbances arising out of change in velocity of flow due to the 

 operation of valves and governors. When a change in velocity of flow is 

 made, a wave of alternate compression and expansion is set up which 

 takes some time to die down, especially if the pipe is a long one, and it 

 is quite possible to obtain widely conflicting results on the same pipe and 

 for the same average flow, due to the operation of the various impulses 

 that may be set up. Another possible source of irregularity is the 

 occlusion of air in larger or smaller quantities due to fluctuations of 

 pressure. This might affect the flow considerably at a given head, whilst 

 the proximity of the gauge to a bend or to a discharge-opening has been 

 found to vitiate the results. That some disturbances of the kind men- 

 tioned are at work will be quite evident on contemplating the graphs 

 showing the results, to which attention will now be drawn. 



Cast-ikon Pipe. 

 A very complete list of experiments on loss of head in cast-iron pipe 

 will be found in Barnes's work, Hydraulic Ftoiv Reviewed, including some 

 particularly careful determinations by the said author himself, which 

 fulfil all the requirements. The examples selected are taken from the 

 publication mentioned. Four experiments by Darcy on clean, new, 

 uncoated cast-iron pipes are represented by a, b, c, and k in tig. 1, the 

 diameters varying from 02678 ft. to 16404 ft. The readings are erratic, 

 and no conclusion can be drawn from them further than that the trend 

 of the observations generally follows the curve for drawn-sceel pipes. 

 The remaining experiments are upon asphalted cast-iron pipes, either 



