d
practical watchmakers could tell you what proportion of a cylinder
should be cut away from the half shell? How many could explain the
difference between the "real" and "apparent" lift? Comparatively few,
and yet a knowledge of these things is as important for a watchmaker as
it is for a surgeon to understand the action of a man's heart or the
relations of the muscles to the bones.

ESSENTIAL PARTS OF THE CYLINDER ESCAPEMENT.

The cylinder escapement is made up of two essential parts, viz.: the
escape wheel and the cylinder. The cylinder escape wheel in all modern
watches has fifteen teeth, although Saunier, in his "Modern Horology,"
delineates a twelve-tooth wheel for apparently no better reason than
because it was more easily drawn. We, in this treatise, will consider
both the theoretical action and the practical construction, but more
particularly the repair of this escapement in a thorough and complete
manner.

At starting out, we will first agree on the names of the several parts
of this escapement, and to aid us in this we will refer to the
accompanying drawings, in which Fig. 122 is a side elevation of a
cylinder complete and ready to have a balance staked on to it. Fig. 123
shows the cylinder removed from the balance collet. Figs. 124 and 125
show the upper and lower plugs removed from the cylinder. Fig. 126 is a
horizontal section of Fig. 122 on the line _i_. Fig. 127 is a side view
of one tooth of a cylinder escape wheel as if seen in the direction of
the arrow _f_ in Fig. 126. Fig. 128 is a top view of two teeth of a
cylinder escape wheel. The names of the several parts usually employed
are as follows:

_A._--Upper or Main Shell.
_A'._--Half Shell.
_A''._--Column.
_A'''._--Small Shell.
_B B' B''._--Balance Collet.
_G._--Upper Plug.
_H._--Lower Plug.
_g._--Entrance Lip of Cylinder.
_h._--Exit Lip of Cylinder.
_c._--Banking Slot.
_C._--Tooth.
_D._--U arm.
_E._--Stalk of Pillar.
_I._--U space.
_l._--Point of Tooth.
_k._--Heel of Tooth.

The cylinder escapement has two engagements or actions, during the
passage of each tooth; that is, one on the outside of the cylinder and
one on the inside of the shell. As we shall show later on, the cylinder
escapement is the only positively dead-beat escapement in use, all
others, even the duplex, having a slight recoil during the