220 OUTLINES OF NATURAL PHILOSOPHY. 



The machine known by the name of BARKER'S Mill is 

 of this kind. Let ABGH, (fig. 24.), be a hollow 

 cylinder, moveable about a vertical axis CD, and 

 having the horizontal boxes EB, EG communica- 

 ting with it, so that the whole may be filled with 

 water from the top. The boxes have each an open- 

 ing in the sides, opposite to one another, through 

 which the water issues. 



When these apertures are shut, and the whole filled 

 with water, it remains in equilibria; but if the 

 apertures are opened, the columns having these aper- 

 tures for their bases, and the depth of the water for 

 their altitudes, will cease to press on the sides ; and 

 therefore the whole pressure on the sides where there 

 are no perforations, will be greater than on the sides 

 where the perforations are, by the sum of these two 

 columns. 



A moving force, therefore, equal to the pressure of 

 these two columns, will impel the machine in a di- 

 rection opposite to that in which the water issues, 

 and in that direction the machine will begin to 

 move. 



312. The moving force in this instance becomes 

 greater, after the machine has begun to move ; for 

 the water in the horizontal boxes acquires a cen- 

 trifugal force, by which its pressure against the 

 sides is increased. When the machine works to 

 the greatest advantage, the centre of the perfora- 



ty _____ 



tions should move with the velocity v hg, 



where 



