as it
must when locked. A tangential locking in the true sense of the meaning
of the phrase is a locking set so that a pallet with its face coinciding
with a radial line like _A G_ would be neutral, and the thrust of the
tooth would be tangent to the circle described by the locking angle of
the tooth. Thus the center _C_, Fig. 86, is placed on the line _w'_
which is tangent to the circle _s_; said line _w'_ also being at right
angles to the radial line _A G_.

The facts are, the problems relating to the club-tooth lever escapement
are very intricate and require very careful analysis, and without such
care the horological student can very readily be misled. Faulty
drawings, when studying such problems, lead to no end of errors, and
practical men who make imperfect drawings lead to the popular phrase,
"Oh, such a matter may be all right in theory, but will not work in
practice." We should always bear in mind that _theory, if right, must
lead practice_.

CORRECT DRAWING REQUIRED.

If we delineate our entrance pallet to have a draw of twelve degrees
when in actual contact with the tooth, and then construct in exact
conformity with such drawings, we will find our lever to "hug the banks"
in every instance. It is inattention to such details which produces the
errors of makers complained of by Saunier in section 696 of his "Modern
Horology," and which he attempts to correct by drawing the locking face
at fifteen degrees draw.

We shall show that neither _C_ nor _C'_, Fig. 85, is the theoretically
correct position for the pallet center for a tangential locking.

We will now take up the consideration of a club-tooth lever escapement
with circular pallets and tangential lockings; but previous to making
the drawings we must decide several points, among which are the
thickness of the pallet arms, which establishes the angular motion of
the escape wheel utilized by such pallet arms, and also the angular
motion imparted to the pallets by the impulse faces of the teeth. We
will, for the present, accept the thickness of the arms as being
equivalent to five degrees of angular extent of the pitch circle of the
escape wheel.

[Illustration: Fig. 87]

[Illustration: Fig. 88]

In making our drawings we commence, as on former occasions, by
establishing the center of our escape wheel at _A_, Fig. 87, and
sweeping the arc _a a_ to represent the pitch circle of such wheel.
Through the center _A_ we draw the vertical line _A B_, wh