The, Mow of Water through Pipes. 341 



* The Flow of Water through Pipes. Experiments on Stream-line 

 Motion and the Measurement of Critical Velocity." By 

 H. T. BAKNES, D.Sc., Assistant Professor of Physics, and 

 E. Gr. COKER, M.A., D.Sc., Associate Professor of Civil Engineer- 

 ing, McGill University. Communicated by Professor OSBURKE 

 KKYNOLDS, F.E.S. Eeceived November 4, Read November 24, 

 1904. 



In a brief note published in the 'Physical Review,'* we have 

 described a thermal method of observing the change from stream-line 

 to eddy motion for water flowing through pipes of different diameters. 

 This method we have recently employed in a series of experiments, 

 which we have carried out on a much larger scale than was previously 

 attempted. The method had several points to recommend it for our 

 particular work, the chief one being the simplicity of the experimental 

 arrangements. The object in undertaking this investigation, for 

 which our method was adapted, was in the interest attached to a study 

 of stream-line flow, where every form of initial disturbance was as 

 completely removed from the water as possible. 



The impossibility of heating a column of water uniformly throughout 

 while flowing in stream-line motion has been previously observed.! 

 It was shown that, when water is heated electrically while flowing 

 through a tube of two or three millimetres in diameter by a central 

 wire conductor, the heat is carried off by the rapidly moving stream, 

 which forms a cloak of hot water around the wire, and leaves the 

 walls of the tube almost entirely unheated. If the heat be applied to 

 the outside of the tube, the heated water remains in contact with the 

 inner surface of the tube and the water flows through the centre of 

 the tube at a much lower temperature. It is quite different if the 

 flow is increased sufficiently to break up the stream-lines. In this case, 

 eddy or sinuous motion results, and the distribution of heat throughout 

 the water column becomes uniform. 



The change from stream-line to eddy motion can be very clearly 

 observed in a tube heated on the outside, since the temperature of the 

 emerging stream immediately increases when the flow rises above 

 the critical point. The point of change is very sharp, and the 

 disappearance of the stream-lines instantaneous. 



At the outset of our work we were guided by the two very im- 

 portant papers of Osborne Reynolds,! in which the laws governing 

 the flow of water in pipes and channels are worked out. It is clear 



* 'Physical Review,' vol. 12, p. 372 (1901). 



f H. T. Barnes, 'Phil. Trans.,' A, vol. 199, p. 234 (1902). 



J 'Phil. Trans., 1882 and 1895. 



