428 MR. RENNIE ON THE FRICTION AND RESISTANCE OF FLUIDS. 
the apparatus was then fixed in an iron frame, and the frame let into a groove 
in two upright posts, driven into the bed of the river Thames. 
The object of the frame was to allow the cylinder to slide up and down 
with the level of the tide, and immerse it more or less according to the expe- 
riment required to be tried. The friction of the apparatus, or the time that 
the weight took to descend in the atmosphere, was first noticed; after which it 
was successively immersed in the water three, six, nine, twelve, fifteen, eighteen, 
twenty-one, and twenty-four inches, the difference of time showing the retarda- 
tion according to the annexed Table. 
Experiments on the Friction of the Surface of a Cylinder, twenty-four inches 
long and ten inches three quarters diameter, moving in air and in water. 
Table I. 
On Surfaces in Water. 
Depth of 
immersion 
of 
cylinder. 
Weight 
suspended. 
Number of 
revolutions of 
cylinder falling 
the whole height 
of 26 feet. 
Time in 
descending 
in water. 
Velocity of 
peri phery 
per second 
in water. 
Time in 
descending 
in air. 
Velocity of 
periphery 
per second 
in air. 
Difference 
between 
air and 
water. 
Remarks. 
inches. 
3 
6 
9 
12 
15 
18 
21 
24 
lbs. 
1 
Sixteen turns in 
descending. 
Periphery moves 
through 540.32 
inches. 
seconds. 
15.00 
18.00 
25.00 
28.00 
32.00 
37.00 
40.00 
55.00 
inches. 
36.021 
30.017 
21.612 
19-297 
16.885 
14.603 
13.508 
9-824 
seconds. 
10 
inches. 
54.032 
seconds. 
5.00 
8.00 
15.00 
18.00 
22.00 
27.00 
30.00 
45.00 
Resistance in- 
creased by sur- 
face with slow 
velocities, but 
not in the ratio 
of the surfaces. 
3 
6 
9 
12 
1 5 
18 
21 
24 
2 
Ditto. 
9-00 
10.00 
10.50 
10.50 
10.50 
10.50 
11.00 
11.00 
60.035 
54.032 
51.459 
51.459 
51.459 
51.459 
49.120 
49-120 
5 
108.064 
4.00 
5.00 
5.50 
5.50 
5.50 
5.50 
6.00 
6.00 
Resistance 
scarcely influ- 
enced by sur- 
face with in- 
creased veloci- 
ties. 
On Velocities in 
Water. 
inches. 
lbs. 
seconds. 
inches. 
seconds. 
inches. 
seconds. 
24 
4 
8.0 
67-54 
2.45 
196.48 
5.15 
24 
8 
Ditto. 
6.0 
90.053 
2.00 
270.16 
4.00 
Could not be 
24 
16 
4.0 
135.08 
1,50 
360.21 
2.50 
24 
32 
2.5 
216.128 
