182 STEELYARD. 



To shew how to graduate the common /, 

 Let AS be the beam of the steelyard. A the fi 



\ 





Qi* 



from winch the substance to be weighed is suspended, Q 

 being its weight; C the fulcrum; H'the weight of the 

 together with the hook or scale-pan suspended from A ; G 

 the centre of gravity of these. 



SupjM).sc that P suspended at .$" balances Q suspended 

 A : then, taking the moments of P, (J, and IT about C T , we 

 have 



therefore 



Q = 



r+ . 



A C 



P. 



Take the point D, so that 



w 



; therefore 



AC 





Now let the arm />/? be gradiiatr-d by taking J 

 Da^ ...... equal respectively to AC, 2AC, 3AC ...... ; let the 



.-a 1, 2, 3, 4, ...... be placed over the points of -rad na- 



tion, and let subdivisions be made between th n ly 



observing the graduation at A' we know the ratio of Q t 

 and P being a given weight we know the weight of Q. In 

 thU way any substance may be w 



-econd of hanical Powers is the Wheel 



and Axle. This machine consists of two cylinders fixed 



