(240 On the Measure of 
of waterirepresented by @X2BC has descénded 
. from B torC, and has: been’ brought’ to’ rest. 
. But the: reaction is =axX2BC, and this 
multiplied by 2BC, the space through which 
‘ithas acted, gives ax2 BC} for the amount 
of the moving force’ produced, which’ js ex- 
2 actly the quantity of moving force necessary 
>to 'raise the column ax 2 BC to the height BC, 
and to projéct it with the velocity 2BC. ‘For, 
“a moving force =ax2BCX BC ‘will raise that 
“golumn from © to B; and an equal moving 
force will generate the velocity 2BCit in the same 
i] 
‘column, therefore 2ux2BCx BC=ax2BC\ 
is the whole moving force necessary to restore 
that column to the” place and condition in 
which it was before it began to descend ; and 
as no moving ‘force has been ekpended in 
producing dnttige of figure, that quantity of 
moving force must be‘ found in the reaction 
of the 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, I apprehend, of 
the action of the hydraulic machine called 
Barker’s mill. Let AB (fig..19) be the per-_ 
pendicular tube, and BC the horizontal arm ; 
let v express, in feet per second, the rotatory 
velocity of the arm at the orifice C, and let the 
