88 FERGUSON'S LECTURES. 



LECT. water acts constantly and uniformly upon it ? The plain 

 ^v / l x>/ answer is, That the velocity of the wheel can never be 

 so great as the velocity of the water that turns it ; for, 

 if it should become so great, the power of the water 

 would be quite lost upon the wheel, and then there would 

 be no proper force to overcome the friction of the geers 

 and attrition of the stones. Therefore, the velocity 

 with which the wheel begins to move, will increase no 

 longer than till its momentum or force is balanced by the 

 resistance of the working parts of the mill ; and then 

 the wheel will go on with an equ a ble motion. 

 i hand- [If the cog-wheel D be made about 18 inches diame- 



*77 



ter, with 30 cogs, the trundle as small in proportion, 

 with 10 staves, and the millstones be each about two feet 

 in diameter, and the whole work be put into a strong 

 frame of wood, as represented in the figure, the engine 

 will be a hand-mill for grinding corn or malt in private 

 families. And then, it may be turned by a winch instead 

 of the wheel A A : the millstone making three revolutions 

 for every one of the winch. If a heavy fly be put upon 

 the axle B, near the winch, it will help to regulate the 

 motion.] 



If the cogs of the wheel and rounds of the trundle 

 could be put in as exactly as the teeth are cut in the 

 wheels and pinions of a clock, then the trundle might 

 divide the wheel exactly : that is to say, the trundle 

 might make a given number of revolutions for one of 

 the wheel, without a fraction. But as any exact number 

 is not necessary in mill-work, and the cogs and rounds 

 cannot be set in so truly as to make all the intervals 

 between them equal ; a skilful mill-wright will always 

 give the wheel what he calls a hunting cog ; that is, one 

 more than what will answer to an exact division of the 

 wheel by the trundle. And then, as every cog comes to 

 the trundle, it will take the next staff or round behind 

 uie one which it took in the former revolution : and by 



