MOVING FORCE. 
‘i97 
in which it was before it began to descend ; and as no moving Ca.>cs of difli- 
force has been expended in producing change of figure, that 'of 
quantity of moving force must be found in the reaction of the moving lorcr. 
water through the space which the vessel has moved while the 
water descended and was brought to rest. 
Upon the same principle an easy and simple explanation may 
be given, r apprehend, of the action of the hydraulic machine 
called llarker’s mill. Let AB (fig lo) be the perpendicular 
tube, and BC the horizontal arm j let v express, in feet per 
second, the rotatory velocity of the arm at the orifice C, and let 
the water be supposed to issue with the velocity due to the 
pressure. Put g= 167 '— feet. 
If BC be a cylindrical tube, and if q represent the quantity 
of water it contains from B to C, the centrifugal pressure upon 
QV^ 
a section of the arm at C, will be — J : and whatever the 
4- BC 
length BC may be, the diameter remaining the same, q being as 
BC, the centrifugal pressure at C will always be as v* ; and it 
will be equal to the pressure of a perpendicular column of water 
whose heiglit in feet is Then if h express in feet the 
4 
r* 
height AB of the water in the vertical tube, A+— will be the 
whole pressure at C ; and if a express in feet the area of the 
most contracted section of the orifice, 2 flf h ) will ex- 
\ 4 " / 
press the reaction, which being multiplied by v, the space 
/ \ 
through which it acts in a second, gives 2av^ h 
total moving force of the arm in a second. But a part of this 
moving force is expended in producing the rotatory motion of 
the water, and in raising it to the height — . For, if we sup- 
4>r 
pose a perpendicular tube CP to rise from the arm at C, the 
surface of the water in that tube would stand at P, PR being 
Now if instead of letting the water esca^^ at C, it be 
allowed 
