[ 45 ] 
III. An Experimental Determination of the Variation loith Temperature of the 
Critical Velocity of Flow of Water in Fipes. 
By E. G. Coker, M.A. {Cantah.), D.Sc. (Edin.), Assistant Professor of Civil 
Engineering, and S. B. Clement, B.Sc. {McGill), Demonstrator in Civil 
Engineering, both of McGill University, Montreal. 
Communicated by Professor Osborne Eeynolds, F.R.S. 
Eeeeived July 16,—Read November 20, 1902. 
1. Introduction. 
The motion of water in pqDes and channels has been the subject of frequent 
investigation, both from the theoretical and the experimental side, and it is well 
known that while in some cases theory and experiment are in exact accord, yet in 
many others the experimental results difiPer Avidely from the calculated. 
In some cases, wliile tlm theory holds for one set of conditions, it is found not to 
hold for conditions which at first do not appear to be fundamentally different. 
A striking instance is that of the flow of a viscous liquid through a pipe of circular 
section, a case for which a strict mathematical solution can be obtained under 
certain assumed conditions of flow. Experiment shows that the theory is verified if 
the pipe IS of capillary bore and the motion small, while if the pipe is large and the 
motion appreciable, there is a large discrepancy between experiment and calculation. 
I he discrejDancy is due to tlie assumption that the motion is stream-line, a condition 
of things whicli is true for tubes of capillary bore, but in general is not true f<;)r 
tubes of apprecialde diameter unless the motion is lieloAv a certain limit, fixed by the 
size of the pipe and the physical characteristics of the liquid. Above this limit, the 
motion is eddying and the hydrodynamical equations no longer apply. 
The change from stream-line to eddy or sinuous motion was first studied by 
Osborne liEVNOLDS,^'' who shoAved that the determining factors in the case of a 
ciicular pipe depended on the dimensions of the pipe and the viscosity of the AAnteiv 
His results are liased partly on deductions from the equations of motion for a viscous 
An Experimental Iiive.stigalion of the Circiimstance.s which determine whether the Motion of Water 
shall be Direct or Sinuous, and of the Law of Resistance in Parallel Channels.” ‘Phil. Trans.,’ 1882 
