Mr. V ince's Observations on the Theory 
same reason the effect of the resistance of the whole. plane a 
at the distance d is as d 3 a; hence d 3 a =flu. x 3 a, consequently 
If the plane be a parallelogram, two of whose sides 
are parallel to the arms, and m and n the least and great- 
est distances of the other two sides from the axis, then 
Now to find the resistance of the planes striking the fluid 
perpendicularly, first set them parallel to the horizon, so that 
they may move edge-ways, or in their own plane, and let two 
equal weights be put, one into each scale, such as to give the 
arms an uniform velocity, and then these weights together (w) 
will be just equivalent to the friction of the axis and the re- 
sistance of the arms. Then place the planes perpendicular to 
the horizon by a plumb-line, and put in two more equal 
weights, one into each scale, making together W, so as to give 
the planes the same uniform velocity as before. Then, from 
what has been already observed, there is no additional friction, 
and therefore this weight W must be equivalent to the resist- 
ance of the planes. But this equivalent weight W acts only 
at the distance of the radius r of the axis from the centre of 
motion, whereas the resistance is to be considered as acting at 
the distance d of the centre of resistance from the centre of 
motion ; hence d : x : : W : yx W the weight acting at the 
distance d, which is equivalent to the resistance acting at the 
same distance, and consequently it must be equal to the abso- 
lute resistance against all the planes. And to find the velocity, 
let C feet be the circumference described by the centre of 
