of Bodies moving in Fluids . 11 
the particles which strike the body at rest, similar to the action 
of the fluid before the body, upon the particles which strike 
the body moving in the fluid. Hence, the resistance of the 
planes moving in the fluid, with the velocity here given, is 
diminished about one fifth part of the whole, by the pressure 
behind the body ; but, with different velocities, this diminution 
must increase as the velocity increases. 
The effect of that part of the force which acts perpendicular 
to the plane being thus established, we proceed next to exa- 
mine, what part of the whole force which acts parallel to the 
plane, is effective. To determine which, the axis zv v (fig. 2.) 
was fixed perpendicular to the plane of the lever abed , and the 
ends of the axis were conical, and laid in conical holes; and the 
thread from which the scale was hung was fixed to the edge 
at e, and acted perpendicular to it and the weight drew the 
lever in the direction e s, contrary to that in which the fluid 
tends to move the lever, and it acted at the same perpendicular 
distance from the axis below, as the fluid acted above it. Let 
xmz be a line parallel to the horizon, when the lever is per- 
pendicular to it, and which passes through the centre of the 
stream ; and let xmz be also the direction of that part of the 
force which acts parallel to the plane. This apparatus being 
adjusted, the experiments were made for every tenth degree of 
inclination ; and here a circumstance took place, for which I 
can give no satisfactory reason. Having gone through the ex- 
periments once, and noted the results, I repeated them ; and, 
to my great surprise, I found all the second results to be very 
different from the first. The experiments were therefore re- 
peated again, and the results were still different. Being certain 
that the experiments were very accurately made each time, I 
C 2 
