MECHANICS. 77 



similar instruments might be constructed. In some 

 of the nicest balances, b is made variable by means 

 of a small moveable weight. 



134. When a balance is false, or its arms une- 

 qual, if any thing be weighed, first in the one 

 scale, and then in the opposite, the true weight is 

 a mean proportional between the weights thus 

 found, or is equal to the square root of their pro- 

 duct. 



Consult LA HIIIE, Tralte de Mechdtnique, prop. 33. 

 MUSCHKNBKOEK, 283, &c. EuLER, Comment. Pe- 

 trop. torn. x. p. 1. &c. MAGELLAN, Journal de 

 torn. xvii. (1781), p. 43, 



Of the JFheel and Axle. 



135. The wheel and axle, consists of a wheel 

 having a cylindric axis passing through its centre, 

 and moveable in two grooves. The power is ap- 

 plied to the circumference of the wheel, and the 

 weight to the circumference of the axle. An 

 equilibrium in this instrument takes place, when 

 the radius of the wheel, multiplied into the power, 

 is equal to the radius of the axle multiplied into 

 the weight ; or when the power and weight are 

 inversely as the radii of the circles to which they 

 are applied. 



ft 



