[ 375 1 



xxvr. 



STEADY AND TUEBULENT MOTION IN GASES. 



By JOHN J. DOWLING, M.A., 



Lecturer in Pliysics, University College, Dublin. 



Plates XXXII. and XXXIII. 



[Eead June 25; published Noyember 16, 1912.] 



Pakt I. 



Introduction. 



Osborne Reynolds/ experimenting with water, showed that at a certain 

 so-called " critical " Yelocity the motion of a liquid through a tube 

 ceased to be a linear flow, and turbulent motion then set in. His results 

 are usually expressed in the form — 



V.-^'^K.. (1) 



pa 



where Vc = the critical velocity, 



T] = the coefficient of viscosity of the fluid, 

 p = the density, 

 a = the radius of the tube. 

 He also gave certain theoretical reasons for his results. His general results 

 were confirmed by later workers. 



Pteynolds^ method of experimenting was to allow water to flow through 



a glass tube, and to observe the behaviour of a thread of coloured 



water introduced by means of a fine delivery tube placed along the axis 



of the larger tube, near one end. At tlie critical velocity tlie turbulence 



manifested itself by dissipating the even thread of colour. He worked 



also on another method, and examined how the volume of water delivered 



by a pipe several feet long depended on the head of pressure causing the 



flow. At first the resistance was proportional to the velocity ; but after the 



critical point was passed the resistance soon varied nearly as the 1"72 power 



of the velocity. The point where the first condition ceased gave the critical 



velocity. 



1 Reynolds, (Phil. Trans. Roy. Soc, vol. clxxiv, 1883). 



SCIENT. PEOC. K.D.S. , VOL. XIII., NO. XXVI. 3L 



