From the intersection of this arc with the line _a_ (at _r_) we lay off on said arc _n_ 2.1" and establish the points _g g'_, which locate the center of the pillars _H H_. With the dividers set so one leg rests at the center _m_ and the other leg at the point _d_, we sweep the arc _t_. With the dividers set at 1.33" we establish on the arc _t_, from the point _d_, the points _e e'_, which locate the position of the pillars _E E'_. The outside diameter of the balance _B_ is 3-5/8" with the rim 3/16" wide and 5/16" deep, with screws in the rim in imitation of the ordinary compensation balance.
Speaking of a balance of this kind suggests to the writer the trouble he experienced in procuring material for a model of this kind--for the balance, a pattern had to be made, then a casting made, then a machinist turned the casting up, as it was too large for an American lathe. A hairspring had to be specially made, inasmuch as a mainspring was too short, the coils too open and, more particularly, did not look well. Pallet jewels had to be made, and lapidists have usually poor ideas of close measurements. Present-day conditions, however, will, no doubt, enable the workman to follow our instructions much more readily.
In case the reader makes the bridges _C_ and _F_, as shown in Fig. 27, he should locate small circles on them to indicate the position of the screws for securing these bridges to the pillars which support them, and also other small circles to indicate the position of the pivot holes _d b_ for the escape wheel and pallet staff. In practice it will be well to draw the line _a a_ through the center of the main plate _A_, as previously directed, and also establish the point _d_ as therein directed.
The pivot hole _d'_ for the escape wheel, and also the holes at _e e_ and _b_, are now drilled in the bridge _F_. These holes should be about 1/16" in diameter. The same sized hole is also drilled in the main plate _A_ at _d_. We now place a nicely-fitting steel pin in the hole _d'_ in the bridge _F_ and let it extend into the hole _d_ in the main plate. We clamp the bridge _F_ to _A_ so the hole _b_ comes central on the line _a_, and using the holes _e e_ in _F_ as guides, drill or mark the corresponding holes _e' e'_ and _b_ in the main plate for the pillars _E E'_ and the pallet staff.