2 Mr. Vince's Experiments on the Resistance 
moves in a fluid, its particles strike the body; and, in our theo- 
retical considerations, after this action, the particles are sup- 
posed to produce no further effect, but are conceived to be, as 
it were, annihilated. But, in fact, this cannot be the case; 
and what we are to allow for their effect afterwards, is beyond 
the reach of mere theoretical investigation. Whatever theory 
therefore we can admit, must be that which is founded upon 
; 
such experiments as include in them every principle which is 
subject to any degree of uncertainty. We must therefore have 
recourse to experiments, in order to establish any conclusions 
upon which we may afterwards reason. In the paper above 
mentioned, I described a machine to find the resistances of 
bodies moving in fluids ; since which time, I have made a va- 
riety of experiments with it, upon bodies moving both in air 
and water, and I have every reason to be satisfied of its great 
accuracy. In this paper, I propose to examine the resistance 
which arises from the action of non-elastic fluids upon bodies. 
This subject divides itself into two parts ; we may consider 
the action of water at rest upon a body moving in it, or we 
may consider the action of the water in motion upon the body 
at rest. We will first give the result of our experiments in the 
former case, and compare them with the conclusions deduced 
from theory. Now the radius of the axis of the machine made 
use of in these experiments was 0,2117 in. the area of the four 
planes was 3,73 in. the distance of their centres of resistance 
from the axis was 7,57 in. and they moved with a velocity of 
o,66 feet in a second. The first column of the following table 
exhibits the angles at which the planes struck the fluid ; the 
second column shows the resistance by experiment, in the 
direction of their motion, in Troy ounces ; the third column 
