NEW BALANCE. 



121 



to be adjusted every time the watch wants cleaning ; I hare 

 rejected this mode altogether, and have contrived a method 

 of applying the direct expansion of metals, which I find 

 by experience to be constant and permanent in its eft'ects. 



My balance consists of a flat steel bar, which forms its The newba- 

 diameter. Beneath this steel bar are two metallic rods, ^a"*^'^^^'^'^"^^'* 

 secured at one end by a stud, formed out of the steel bar, 

 and the other end acting on the short end of a lever, formed 

 out of the other end of the same steel bar, being made to 

 spring at the place where the centr*: of the lever would 

 fall; to this lever is fastened a small cylindrical stem of 

 brass, upon which a small globe of brass slides or scrcAvs ; 

 there is also a screw passing through the stem, to serve to 

 regulate to mean time. Another metallic bar, equal and 

 similar, and furnished like the other, but reversed in posi- 

 tion, is placed parallel to it. 



Mode of acting. 

 When the whole balance is heated, the metallic tods will Action of the 

 push forward the short ends of the leveVs, and which "^^ balance 

 quantity will be just equal to the difference of the expansion ^^^ **°^ * 

 of the two metals. Suppose the short ends of the two levers 

 to be each equal to 1, and the long ends of the levers to be 

 each equal to 20, then it is evident that the motion of each 

 globe will be twenty times the excess of the steel bar and 

 metallic rods nearer to the centre of the axis of the balance, 

 than before the expansion took place ; and, what is a very 

 grand and necessary property in the motion of the two 

 globes, they will always move directly to the axis of the 

 balance ; that is, their action will be constantly in a plane, 

 passing through the axis of the globes and axis of the balance. 

 To increase or diminish the expansion of the balance, will 

 be only to slide or screw up or down the globes upon 

 their stems, until the balance produces the desired ciTect, 



Additional Rehiarks on the Balance no'oi in Use. • 



The rim of l)rass an 1 steel of the common balance, how- Manner m 



ever intimately connoctea when first fluxed together, are by rommon ex- 



every change of temperature endeavouring to break the Pension ba- 



eonnection, and do by little and little tear themselves '^"",'^ *^^; 

 , , . . , , ■ posed to fail, 



asunder, at least in a partial degree, for the fracture is 



Vol. XVI,~Feb. 1807. M often 



