OF WATER-MILLS. 85 



height of the fall in feet, and the square root of the pro- LECT. 

 duct shall be the velocity of the water at the bottom of ^^^ 

 the fall, or the number of feet that the water there moves 

 per second. 



3. Divide the velocity of the water fay 3, and the 

 quotient shall be the velocity of the floatboards 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 shall be the number of seconds in which the 

 wheel turns round. 



5. By this last number of seconds divide 60; and the 

 quotient shall be the number of turns of the wheel in a 

 minute. 



6. Divide 60 (the number of revolutions the millstone 

 ought to have in a minute) by the number of turns of 

 the wheel in a minute, and the quotient shall be the num- 

 ber of turns the millstone 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 millstone 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 I have calculated the following table 

 to a water-wheel 18 feet diameter, which I apprehend 

 may be a good size in general. 



To construct a mill by this table, find the height of 

 the fall of water itr the first column, and against that 

 height, in the sixth column, you have the number of cogs 

 in the wheel, and staves in the trundle, for causing the 

 millstone to make about 60 revolutions in a minute, as 

 near as possible, when the wheel goes with a third part 

 of the velocity of the water. And it appears by the 



