These frictional escapements held favor with many eminent watchmakers
even after the introduction of the detached escapements. It is no more
than natural we should inquire, why? The idea with the advocates of the
frictional rest escapements was, the friction of the tooth acted as a
_corrective_, and led no doubt to the introduction of going-barrel
watches. To illustrate, suppose in a cylinder watch we increase the
motive power, such increase of power would not, as in the verge
escapement, increase the rapidity of the vibrations; it might, in fact,
cause the timepiece to run slower from the increased friction of the
escape-wheel tooth on the cylinder; also, in the duplex escapement the
friction of the locking tooth on the staff retards the vibrations.
Dr. Hooke, the inventor of the balance spring, soon discovered it could
be manipulated to isochronism, i.e., so arcs of different extent would
be formed in equal time. Of course, the friction-rest escapement
requiring a spring to possess different properties from one which would
be isochronal with a perfectly detached escapement, these two frictional
escapements also differing, the duplex requiring other properties from
what would isochronize a spring for a cylinder escapement.
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