[Illustration:  Fig. 23]

From the intersection of the line B e with the arc i we lay off two and a half degrees on said arc, and through the point so established we draw the line B g.  The intersection of this line with the arc k we name the point z.  With one leg of our dividers set at A we sweep the arc l so it passes through the point z.  This last arc defines the addendum of the escape-wheel teeth.  From the point r on the arc a we lay off three and a half degrees, and through the point so established draw the line A j.

LOCATING THE OUTER ANGLE OF THE IMPULSE PLANES.

The intersection of this line with the addendum arc l locates the outer angle of the impulse planes of the teeth, and we name it the point x.  From the point r we lay off on the arc a seven degrees and establish the point v, which defines the extent of the angular motion of the escape wheel utilized by pallet.  Through the point v, from B as a center, we sweep the short arc m.  It will be evident on a moment’s reflection that this arc m must represent the path of movement of the outer angle of the exit pallet, and if we measure down ten degrees from the intersection of the arc l with the arc m, the point so established (which we name the point s) must be the exact position of the outer angle of the pallet during locking.  We have a measure of ten degrees on the arc m, between the lines B g and B h, and by taking this space in the dividers and setting one leg at the intersection of the arc l with the arc m, and measuring down on m, we establish the point s.  Drawing a line from point n to point s we define the impulse face of the pallet.

MAKING AN ESCAPEMENT MODEL.

[Illustration:  Fig. 24]

It is next proposed we apply the theories we have been considering and make an enlarged model of an escapement, as shown at Figs. 24 and 25.  This model is supposed to have an escape wheel one-fifth the size of the 10” one we have been drawing.  In the accompanying cuts are shown only the main plate and bridges in full lines, while the positions of the escape wheel and balance are indicated by the dotted circles I B.  The cuts are to no precise scale, but were reduced from a full-size drawing for convenience in printing.  We shall give exact dimensions, however, so there will be no difficulty in carrying out our instructions in construction.

[Illustration:  Fig. 25]