Time and Clocks: A Description of Ancient and Modern Methods of Measuring TimeCunynghame, Henry H. (Henry Hardinge), Sir
Philosophy
Time and Clocks: A Description of Ancient and Modern Methods of Measuring Time
Cunynghame, Henry H. (Henry Hardinge), Sir
Clocks and watches; Time
The crown wheel fell into disuse and was replaced by the anchor
escapement, which was employed in that popular and excellent timepiece
used throughout the eighteenth and the early part of the nineteenth
century, and is now known as “The Grandfather’s Clock.” It was after
all the crown wheel in another shape. The wheel, however, was flattened
out, the teeth being put in the same plane. This made it much easier to
construct. The pallets were fixed on an axis, and were a little altered
so as to suit the changed arrangement of the teeth. The pendulum was
no longer hung on the axis which carried the pallets. A cause of a good
deal of friction and loss of power was thus removed. The pendulum was
hung from a strip of thin steel spring, which allowed it to oscillate,
and which supported it without friction. This excellent manner of
suspending pendulums is now universal. It enabled the pendulum to be
made very heavy. The bob was usually some eight or nine pounds weight.
By this means the acceleration on the pendulum was due almost entirely
to gravity acting on the bob, and thus the motion of the pendulum
became almost wholly harmonic. Whence it followed that variations in
the pendulum swing became of secondary importance, and did not greatly
alter the going of the clock.
[Illustration: FIG. 44.]
Therefore when the wheels became worn, and the pivots choked with old
oil and dust, the old clock still went on. If it showed a tendency to
stop for want of power, a little more was added to the driving weight,
and the clock kept as good time as ever.
The swing of the pendulum was by this escapement enabled to be made
small, so that the arc of swing of the bob differed but little from a
cycloid.
The secret of the time-keeping qualities of these old “Grandfather”
clocks is the length of pendulum. This renders it possible to have
but a small arc of oscillation, and therefore the motion is kept very
nearly harmonic. For practical purposes nothing will even now beat
these old clocks, of which one should be in every house. At present
the tendency is to abolish them and to substitute American clocks with
very short pendulums, which never can keep good time. They are made
of stamped metal. When they get out of order no one thinks of having
them mended. They are thrown into the ash-pit and a new one bought. In
reality this is not economy.
Good “Grandfather” clocks are not now often made. The last place I
remember to have seen them being manufactured is at Morez, in the
district of the Jura. An excellent clock, enclosed in a dust-tight iron
case, with a tall painted case of quaint old design, can be bought for
about 55_s._ The wheels are well cut, and the internal mechanism very
good.
Public-domain text, read in full here on John Shaqi.
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