scale, and from the intersection of B b’ with j we lay off five degrees and draw the line B s’, which establishes the point s on the arc k.  As stated above, we allow one degree for lock, which we establish on the arc o by laying off one degree on the arc j below its intersection with the line B b.  We do not show this line in the drawing, from the fact that it comes so near to B b’ that it would confuse the reader.  Above the arc a on the arc k at five degrees from the point n we establish the point l, by laying off five degrees on the arc j above the intersection of the line B b with j.

The point l, Fig. 90, establishes where the outer angle of the tooth will pass the arc k to give five degrees of angular motion to the lever.  From A as a center we sweep the arc m, passing through the point l.  The intersection of the arc m with the line A h we call the point r, and by drawing the right line r f we delineate the impulse face of the tooth.  On the arc o and one degree below its intersection with the line B b we establish the point t, and by drawing a right line from t to s we delineate the impulse face of our entrance pallet.

“ACTION” DRAWINGS.

One great fault with most of our text books on horology lies in the fact that when dealing with the detached lever escapement the drawings show only the position of the pallets when locked, and many of the conditions assumed are arrived at by mental processes, without making the proper drawings to show the actual relation of the parts at the time such conditions exist.  For illustration, it is often urged that there is a time in the action of the club-tooth lever escapement action when the incline on the tooth and the incline on the pallet present parallel surfaces, and consequently endure excessive friction, especially if the oil is a little thickened.

We propose to make drawings to show the exact position and relation of the entrance pallet and tooth at three intervals viz:  (1) Locked; (2) the position of the parts when the lever has performed one-half of its angular motion; (3) when half of the impulse face of the tooth has passed the pallet.  The position of the entrance pallet when locked is sufficiently well shown in Fig. 90 to give a correct idea of the relations with the entrance pallet; and to conform to statement (2), as above.  We will now delineate the entrance pallet, not in actual contact, however, with the pallet, because if we did so the lines we employed would become confused.  The methods we use are such that we can delineate with absolute correctness either a pallet or tooth at any point in its angular motion.