39 
of the Motion and Resistance of Fluids. 
away the scale D and balance the cylinder when filled, and 
let the end C of the beam be made flat at the point from which 
the vessel is suspended. Then open the orifice of the vessel, 
having the same provision as before to keep it filled to the 
same altitude, and place such a weight at C as shall preserve 
the equilibrium during the time the fluid is in motion, and this 
weight is equivalent to w in the former case. This method is 
the most simple of the two ; but the other includes a cir- 
cumstance of some consequence, that is, that the momentum 
of the effluent fluid is exactly equivalent to the weight which 
the vessel loses. Having thus examined all the circumstances 
which I proposed respecting the emptying of vessels, I proceed 
next to the consideration of the doctrine of the resistance of 
bodies moving in fluids. 
When a body moves in a fluid, each particle, in theory, is 
supposed to act upon it undisturbed by the rest, or the fluid is 
conceived to act as if each particle, after the stroke, were anni- 
hilated, in which case the following particles would exert their 
force uninterruptedly. This supposition is very far from be- 
ing true in fact, and accordingly we find very little agreement 
between theory and experiment. To experiments therefore 
we must have recourse for any thing satisfactory upon this 
subject. I therefore constructed the machine which is here de- 
scribed, whereby both the absolute quantity of resistance in 
all cases may be very accurately determined, and the law of 
its variation under different degrees of velocity. 
AB, CD (Tab. IV. fig. 9.) are two cross pieces of wood 
firmly connected together, with screws at each end, so that it 
may be fixed upon any plane ; E G F is a frame fixed upon 
AB; mn a small, cylindrical well polished iron axis, having 
