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 process of
escaping.
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