950 
MR. 0. REYNOLDS ON THE MOTION OF WATER AND OF 
could hope to perceive what was going on with the naked eye, expecting confidently 
that eddies would make their appearance at an easily attained velocity. 
19. The Jirst apparatus .—This consisted of a tube about ^ inch or 6 millims. in 
diameter. This was bent into the siphon form having one straight limb about 2 feet 
long and the other about 5 feet (Plate 72, fig. 10). 
The end of the shorter limb was expanded to a bell mouth, while the longer end 
was provided with an indiarubber extension on which was a screw clip. 
The bell-mouthed limb was held vertically in the middle of a beaker with the 
mouth several inches from the bottom as shown in figs. 10 and 10'. 
A colour tube about 6 millims. in diameter also of siphon form was placed as shown 
in the figure, with the open end of the shorter limb just under the bell mouth, the 
longer limb communicating through a controlling clip with a reservoir of highly 
coloured water placed at a sufficient height. A supply-pipe was led into the beaker 
for the purpose of filling it; but not with the idea of maintaining it full, as it seemed 
probable that the inflowing water would create too much disturbance, experience 
having shown how important perfect internal rest is to successful experiments with 
coloured water. 
20. The first experiment .—The vessels and the siphons having been filled and 
allowed to stand for some hours so as to allow all internal notion to cease, the colour 
clip was opened so as to allow the colour to emerge slowly below the bell (Plate 73, 
fig. 11). 
Then the clip on the running pipe was opened very gradually. The water was 
drawn in at the bell mouth, and the coloured water entered, at first taking the 
form of a candle flame (Plate 73, fig. 12), which continually elongated until it 
became a very fine streak, contracting immediately on leaving the colour-tube and 
extending all along the tube from the bell mouth to the outlet (fig. 10). On further 
opening the regulating clip so as to increase the velocity of flow, the supply of colour 
remaining unaltered, the only effect was to diminish the thickness of the colour band. 
This was again increased by increasing the supply of colour, and so on until the 
velocity was the greatest that circumstances would allow—until the clip was fully 
open. Still the colour band was perfectly clear and definite throughout the tube. 
It w T as apparent that if there were to be eddies it must be at a higher velocity. 
To obtain this about 2 feet more were added to the longer leg of the siphon which 
brought it down to the floor. 
On trying the experiment with this addition the colour band was still clear and 
undisturbed. 
So that for want of power to obtain greater velocity this experiment failed to show 
eddies. 
When the supply pipe which filled the beaker was kept running during the experi¬ 
ment, it kept the water in the beaker in a certain state of disturbance. The effect ol 
this disturbance was to disturb the colour band in the tube, but it was extremely 
