OF MILLS. 75 



the bottom of the fall, or the number of feet that 

 the water there moves per second. 



3. Divide the velocity of the water by three, 

 and the quotient will be the velocity of the float- 

 boards of the wheel, or the number of feet they 

 must each go through in a second, when the water 

 acts upon them so as to have the greatest power to 

 turn the mill. 



4. Divide the circumference of the wheel in feet 

 by the velocity of its floats in feet per second, and 

 the quotient will be the number of seconds in 

 which the wheel turns round. 



5. By this last number of seconds divide 60, 

 and the quotient will be the number of turns of 

 the wheel in a minute. 



6. Divide 120 (the number of revolutions a mill- 

 stone four feet and a half diameter ought to have 

 in a minute) by the number of turns of the wheel 

 in a minute, and the quotient will be the number of 

 turns the mill-stone ought to have for one turn of 

 the wheel. 



7. Then, as the number of turns of the wheel in 

 a minute is to the number of turns of the mill- 

 stone in a minute, so must the number of staves 

 in the trundle be to the number of cogs in the 

 wheel, in the nearest whole numbers that can be 

 found. 



By these rules, the following table is calculated 

 to a water-wheel 18 feet diameter, which may be a 

 good size in general. 



