45 
of the Motion and Resistance of Fluids. 
resistances with these two velocities of 1 : 2 will be as W : Q. 
If R be the sum of the two equal weights put into the scales to 
give an uniform velocity three times as great as that of the first, 
then with velocities as 1 : 3 the resistances will be as W : R ; 
and so on. This method was proposed by Mr. Robins, in order 
to determine the law of resistance in terms of the velocity. If 
the planes be set at any angle, we can by this means get, in 
terms of the velocity, the law of resistance not only in the di- 
rection of the motion of the planes, but also in a direction per- 
pendicular to that of their motion. An account of all the ex- 
periments which can be made by this machine, some of which 
I believe have never yet been attempted, I shall lay before the 
Royal Society at a future opportunity. 
