In making this drawing we proceed as with Fig. 132 by establishing a center for our radius of 10” outside of our drawing paper and drawing the line A A to such center and sweeping the arcs a b c.  We establish the point e, which represents the center of our cylinder, as before.  We take the space to represent the radial extent of the outside of our cylinder in our dividers and from e as a center sweep a fine pencil line, represented by the dotted line t in our drawing; and where this circle intersects the arc a we name it the point s; and it is at this point the heel of our escape-wheel tooth must part with the exit lip of the cylinder.  From e as a center and through the point s we draw the line e l’’.  With our dividers set to the radius of any convenient arc which we have divided into degrees, we sweep the short arc d’.  The intersection of this arc with the line e l’’ we name the point u; and from e as a center we draw the radial line e u f’.  We place the letter f’’ in connection with this line because it (the line) bears the same relations to the half shell of the cylinder shown in Fig. 133 that the line f does to the half shell (D) shown in Fig. 132.  We draw the line f’’ f’’’, Fig. 133, which divides the cylinder into two segments of 180 degrees each.  We take the same space in our dividers with which we swept the interior of the cylinder in Fig. 132 and sweep the circle v, Fig. 133.  From e as a center we sweep the short arc d’’, Fig. 133, and from its intersection of the line f’’ we lay off six degrees on said arc d’’ and draw the line e’ k’’, which defines the angular extent of our entrance lip to the half shell of the cylinder in Fig. 133.  We draw the full lines of the cylinder as shown.

We next delineate the heel of the tooth which has just passed out of the cylinder, as shown at D’, Fig. 133.  We now have a drawing showing the position of the half shell of the cylinder just as the tooth has passed the exit lip.  This drawing also represents the position of the half shell of the cylinder when the tooth rests against it on the outside.  If we should make a drawing of an escape-wheel tooth shaped exactly as the one shown at Fig. 132 and the point of the tooth resting at x, we would show the position of a tooth encountering the cylinder after a tooth which has been engaged in the inside of the shell has passed out.  By following the instructions now given, we can delineate a tooth in any of its relations with the cylinder shell.

DELINEATING AN ESCAPE-WHEEL TOOTH WHILE IN ACTION.