98 On Water-iV heels 
Let it be supposed that the axle of a wheel is furnished with 
six equidistant planes projecting from the axis, at right angles 
to the line of its direction, in the form of a common water-wheel. 
If the axle be made to rest upon the surface of stagnant water, 
and the wheel be made to revolve quickly through the fluid ; the 
water, which is displaced by the lower planes, will be replaced 
by the contiguous particles of water from the front, from below, 
and from either side. Three of the planes will pass through 
the fluid at the same time, and the motion of the wheel will be 
much more resisted than if each of the planes could be made to 
pass singly through the fluid at separate times. But, of the 
three planes passing through the fluid at the same time, the one 
which has just entered the water, and the other which is just 
going to emerge from the water, have both together very little 
tendency to impel the axle along the surface’; their waste of 
power more than counterbalances “their efficient power. 
Let a wheel have its axis in the diameter of a hollow cylinder, 
and be made to revolve through water at the depth of the axle ; 
the water, extruded by the planes, can only be replaced through 
the front passage: there can be no lateral currents; the water 
in front will be lowered by being drawn into the cylinder by the 
moving planes, and the water behind will be raised by the quan- 
tities forced out in that direction; both of which effects will 
tend to cause a movement of the machine along the surface of 
the sustaining water. In this state of a wheel, any number of 
planes will scarcely augment the resistance to motion, for the 
water will be driven through the cylinder by the advanced plane 
with the velocity of that plane; and the current which follows, 
will be caused by the lateral pressure cf the fluid only: therefore 
the retired planes will find the requisite velocity < already com= 
municated to the water with which they first come in contact, 
and will move in concert with the stream, unresisted in any 
perceptible degree, till they, successively being brought in ad- 
vance, will exercise alternately a similar function, of : acting by 
a separate impulse against the resisting fluid. Under these cir 
cumstances, the resistance to motion will be the pressure of 
water upon the area of asingle plane. The horizontal per- 
cussion of a descending plane against the surface of the fluid 
will be imperceptible, and exempt from all those inconveniences 
which would result from the same act of a wheel moving in free 
water. 
Again, let three parts of a case be strongly connected to- 
gether, namely, a flat bottom and two sides, and let the axle 
of a wheel be supported in the sides so as to revolve clear of 
the hottom. Let the top of the case be a curved plate drawn 
over the sides, air-tight, and made to deseend both ways, 
' round 
