76 



FERGUSON'S LECTURES. 



LECT. 

 III. 



the wheel Chave a 

 ' screw a b on it axis, 

 working in the 

 teetli of the wheel 

 D, which suppose 

 to be 48 in number. 

 It is plain, that 

 for every time the 

 wheel C and screw 

 abare turned round 

 by the winch A, the 

 wheel D will be 

 moved one tooth 

 by the screw ; and 

 therefore, in 48 revolutions of the winch, the wheel D will 

 be turned once round. Then, if the circumference of a 

 circle described by the handle of the winch A be equal to 

 the circumference of a groove e round the wheel D, the 

 velocity of the handle will be 48 times as great as the 

 velocity of any given point in the groove. Consequently, 

 if a line G (above number 48) goes round the groove e, 

 and has a weight of 48 pounds hung to it below the 

 pedestal FF, a power equal to one pound at the handle 

 will balance and support the weight. To prove this by 

 experiment, let the circumferences of the grooves of the 

 wheels C and D be equal to one another ; and then if a 

 weight H of one pound be suspended by a line going 

 round the groove of the wheel C. it will balance a 

 weight of 48 pounds hanging by the line G; and a 

 small addition to the weight H will cause it to descend, 

 and so raise up the other weight. 



If the line G, instead of going round the groove e of 

 the wheel D, goes round its axle /; the power of the 

 machine will be as much increased, as the circumference 

 of the groove e exceeds the circumference of the axle : 

 which, supposing it to be six times, then one pound at 



