430 MR. RENNIE ON THE FRICTION AND RESISTANCE OF FLUIDS. 
Conclusions . 
That the friction or adhesion of water is not quite as the surfaces with slow velocities, being in the 
ratio of one to three instead of one to four, but diminishes rapidly, without observing any ratio in 
increased velocities*. Hence the resistance of a ship or vessel moving through the water, with an 
average or higher rate of velocity, forms an inconsiderable portion of the resistance resulting from the 
displacement of the fluid, and that the brightness observed on the copper of ships after a voyage, may 
be owing to other causes than the friction of the water simply. 
An experiment was made to ascertain the comparative resistance of a pipe 
revolving in water, and with water running through a pipe ; when the resist- 
ance was found to be as the surfaces in slow velocities, but to diminish greatly, 
as before, in high velocities, without observing any fixed ratio. 
The above conclusions are in contradiction to those of Coulomb, who did 
not find that pressure augmented the resistance, but states that the resistance 
is greater when the immersion is partial. 
This apparatus being applicable to fluids generally, advantage was taken of it 
to ascertain the direct resistance of solids to fluids (see Plate XII.)'j~, by causing 
plates and globes to revolve in them, with their planes perpendicular to the 
plane of the horizon. 
As the resistance of solids in fluids does not form the object of this paper, it 
will be unnecessary to introduce many detailed observations on the subject of 
these experiments at present, connected as they are with another branch of 
hydrodynamics. But as it is important to show the relation subsisting be- 
tween the resistances of cohesion and impulse, I have ventured to detail the 
following experiments. 
* The experiments of the Society for the Improvement of Naval Architecture show a decreased 
resistance with increased velocities. 
f In this case, the number of particles struck will be diminished in the ratio of the radius to the sine 
of inclination ; wherefore the resistance will be diminished in a duplicate ratio of the radius to the sine 
of inclination. But as the sines of inclination of the two plates are equal, the resistances will be equi- 
valent to the area of one plate (moving perpendicularly to its planes) into the duplicate ratio of the 
velocity of its motion, and the density of the fluid. 
