The next important step was the use of a count-wheel driven by the pendulum
to give the pendulum an impulse at fixed intervals. The same count-wheel as
already invented by Hipp about 50 years before and used by De Jong in 1865.
Campiche
In 1893 Henri Alfred and Moïse Alexandre Campiche of Geneva fitted a little
pawl to their pendulum pushing a count-wheel tooth
by tooth and impulsing the pendulum at fixed intervals (patent no. 8830).
In 1899 they greatly improved their system by making the
impulse less dependent on the condition of the battery (patent no.10393). animation
At one-minute intervals, a vane attached to the arbor of the count-wheel
slides between two contact springs. The electro-magnet
is energized attracting its armature and the potential energy stored in a spring
is released to the pendulum.
William Edgar Palmer (1864-1951)
In 1902 William Edgar Palmer of Tonbridge, Kent,
devised a similar system (patent no.10541) to that of the Campiche brothers.
At half-minute intervals
a pin fixed to the count-wheel unlatches a catch
holding the gravity arm. The pendulum is now impulsed by means of an impulse
pin fixed to the gravity arm. The last thing the gravity arm does at the end
of its fall is to unlatch a spring, which snaps into contact with a contact-plate
fitted to the gravity arm. The electro-magnet now resets the gravity arm by
means of its armature. animation
Thus the energy for contact making comes from the gravity arm and is not taken
from the pendulum.
Palmer's impulse system is open to the same objections as many other clocks.
Shock and vibration of the pendulum will result, unless the release of the
gravity arm is accomplished at exactly the right moment. In conditions of
variable arc this is found to be practically impossible.
Frank Hope-Jones
In 1905 Hope-Jones took out patent no.6066 in which
he used a count-wheel releasing a gravity arm to impulse the pendulum.
In this patent the impulse system used is still similar to that of the Campiche
brothers.
Three years later in 1908, he devised a far better system (patent no.1945) in
which the method of impulsing was drastically improved.
A vane
fixed to the count-wheel releases the gravity arm at half minute intervals and
a roller fitted to the gravity arm then falls down on a bracket of the pendulum
and impulses the pendulum. When the gravity arm touches a contact screw of the
armature the electro-magnet is energized and its armature throws the gravity
arm back onto its catch.
All the pendulum has to do is to turn the count-wheel and unhook the gravity arm.
The energy lost in doing so is negligible.
The most significant improvement to the impulsing devise is that it is done
very gently and occurs when the pendulum is passing through its zero position
when its kinetic energy is at its maximum and the interference to the freedom
of the pendulum is kept to a minimum. The form of the impulse bracket accomplishes that the impulse always comes at
the right moment when the pendulum is going through its zero position. If
the gravity arm is released too early, the roller of the gravity arm will
just ride on the horizontal plane of the impulse bracket and will not disturb
the freedom of the pendulum.
We now know this system as the "Synchronome switch”.
Hope-Jones used a pendulum rod made of invar. Invar is a nickel-steel alloy
with an extremely low coefficient of expansion invented in 1904 by Charles-Edouard
Guillaume (1861-1938), a Swiss physicist who in 1920 was awarded the
Nobel prize in physics and who's French grand-father was a clockmaker in London.
Using an invar pendulum rod, Hope-Jones' clock of 1908 was capable of outperforming
all but the most accurate astronomical clocks at that time.
Henri Alfred and Moïse Alexandre Campiche of Geneva fitted a little
pawl to their pendulum pushing a count-wheel tooth
by tooth and impulsing the pendulum at fixed intervals (patent no. 8830).
holding the gravity arm. The pendulum is now impulsed by means of an impulse
pin fixed to the gravity arm. The last thing the gravity arm does at the end
of its fall is to unlatch a spring, which snaps into contact with a contact-plate
fitted to the gravity arm. The electro-magnet now resets the gravity arm by
means of its armature. 
