942 
MR. O. REYNOLDS ON THE MOTION OF WATER AND OF 
tubes were immersed, arrangements being made so that a streak or streaks of highly 
coloured water entered the tubes with the clear water. 
The general results were as follows :— 
(1.) When the velocities were sufficiently low, the streak of colour extended in a 
beautiful straight line through the tube, fig. 3. 
Fig. 3. 
(2.) If the water in the tank had not quite settled to rest, at sufficiently low 
velocities, the streak would shift about the tube, but there was no appearance of 
sinuosity. 
(3.) As the velocity was increased by small stages, at some point in the tube, always 
at a considerable distance from the trumpet or intake, the colour band would all at 
once mix up with the surrounding water, and fill the rest of the tube with a mass of 
coloured water, as in fig. 4. 
Fig. 4. 
Any increase in the velocity caused the point of break down to approach the 
trumpet, but with no velocities that were tried did it reach this. 
On viewing the tube by the light of an electric spark, the mass of colour resolved 
itself into a mass of more or less distinct curls, showing eddies, as in fig. 5. 
Fig. 5. 
The experiments thus seemed to settle questions 3 and 4 in the affirmative, the 
existence of eddies and a critical velocity. 
They also settled in the negative question 6, as to the eddies coming in gradually 
after the critical velocity was reached. 
In order to obtain an answer to question 5, as to the law of the critical velocity, 
the diameters of the tubes were carefully measured, also the temperature of the 
water, and the rate of discharge. 
(4.) It was then found that, with water at a constant temperature, and the tank 
as still as could by any means be brought about, the critical velocities at which the 
