[ 289 ] 



XXVIII. 



NOTE ON THE OKIGINATION OF TUEBULENT MOTION IN 

 VISCOUS LIQUIDS. By G. F. FITZ GEEALD, F.T.C.D. 



[Read January 9, 1889.] 



In a viscous liquid moving near a fixed surface the motion is 

 laminar if the rate of change of motion with distance from sur- 

 face is not too great. Under these circumstances a small devia- 

 tion from laminar motion is gradually destroyed by the viscosity. 

 If we consider the forces acting on any wave supposed superadded 

 to the laminar motion, we see that the pressure, on what may be 

 called the windward side of the wave, is greater than on the lee 

 side on account of the viscosity of the liquid ; and if the change of 

 velocity of the liquid with distance from surface be great enough, 

 the difference of pressure may be great enough to cause the wave 

 to become greater and greater notwithstanding viscosity, just as 

 the wind causes waves in the sea, and the waves will ultimately 

 break, which corresponds to a production of turbulent motion. If 

 the waves, originally produced be of short wave length, they would 

 be more affected by the viscosity stopping them than larger ones, 

 and so only turbulency of a definite size would be produced. This 

 theory seems to account for most of Professor Osborne Eeynolds' 

 observations. 



SCIEN. PROC. ll.D.S. — VOL. VI., PT. VI. 



2A 



