422 SUPPLEMENT. 



The hoop or case that goes round the mill-stone rests 

 on the floor K, and supports the hopper, in the common 

 way. The lower end of the spindle turns in a hole in 

 the bridge-tree G F, which supports the mill-stone, 

 tube, spindle, and trunk. This tree is moveable on a 

 pin at h, and its other end is supported by an iron-rod 

 N fixed into it, the top of the rod going through the 

 fixed bracket O, and having a screw-nut o upon it, 

 above the bracket. By turning this nut forward or back- 

 ward, the mill-stone is raised or lowered at pleasure. 



Whilst the tube B is kept full of water from the 

 pipe A, and the water continues to run out from the 

 ends of the trunk; the upper mill-stone H, together 

 with the trunk, tube, and spindle, turns round. But, if 

 the holes in the trunk were stopped, no motion would 

 ensue ; even though the tube and trunk were full of 

 water. For, 



If there were no hole in the trunk, the pressure of 

 the water would be equal against all parts of its sides 

 within. But, when the water has free egress through 

 the holes, its pressure there is entirely removed : and 

 the pressure against the parts of the sides which are 

 opposite to the holes, turns the machine. 119 



A Machine for demonstrating that, on equal Bottoms, the 

 Pressure of Fluids is in Proportion to their perpendicular 

 Heights, without any regard to their Quantities. 



This is termed The Hydrostatical Paradox ; and the 

 machine for shewing it is represented thus : in which 



Note 129. The power of a mill, constructed on this principle, will 

 depend on the height of the column of water allowed to press on th 



horizontal trunk c. 



