C. Paul's new Steel-Yard. 409 



ftruments might be fubitituted with advantage for common 

 balances. In order that I mav better explain in what the 

 improvements of the fteel-yards fubmitted to the Society 

 confifi, it will be proper to point out what were the faults 

 •of the common ones. 



1. There were none of them, in which the points of fuf-r 

 penfion were exacr.lv in the prolongation of the line of the 

 divifions of the beam ; a circumitance which neceffarily 

 changed the relation between the arms of the lever, the 

 power and the refiftance, according as the direction of the 

 beam was changed from a horizontal pofition. We have 

 feen fteel-yards, in which a degree only of difference in the 

 inclination of the beam produced the difference of more 

 than a pound in the refult. 



2. When the fhcll, the beam, and weight, are made at 

 hazard, a perfon who poffeffes a fteel-yard cannot know 

 when the inftrument is deranged; and even an artift cannot 

 repair it, but by repeated trials, and with a great lofs of 

 time. 



3. The c-onftrudtion of the common fteel-yards, which 

 have a fmall and a large fide, renders it neceffrry to invert 

 them frequently : a laborious operation when thefe inftru- 

 ments are heavy, and which expofes the axes to the danger 

 of damage by the effeft of the (hocks which that turning 

 occafions. 



As thefe double fides renders it necefiary to have a beam 

 very firaight, in order that it may be lefs faulty, it readily 

 bends, which is a new fource of error; and, the face which 

 bears the numbers being narrow in proportion, it is difficult 

 to form on it numbers fufHciently vhible. Thefe inconve- 

 niences are all avoided by the eonftruction of (.'. Paul, which 

 prefents, befides, feveraj other advantages not poflefled by the 

 old (leel-yards. 



1. The centres of the movement of fufpenfion, or the two 

 conflant centres, are placed on the exact line of the divifions of 

 the beam ; an elevation almoil imperceptible in the axi.-. of 



the 



